Clarify our OOP semantics across the codebase (#9586)

Basically: * Use `extend` for class definitions * Use `new` for object instantiations That includes some minor code cleanups along the way: * Updated `Widget`'s docs to make the semantics clearer. * Removed `should_restrict_JIT` (it's been dead code since https://github.com/koreader/android-luajit-launcher/pull/283) * Minor refactoring of LuaSettings/LuaData/LuaDefaults/DocSettings to behave (mostly, they are instantiated via `open` instead of `new`) like everything else and handle inheritance properly (i.e., DocSettings is now a proper LuaSettings subclass). * Default to `WidgetContainer` instead of `InputContainer` for stuff that doesn't actually setup key/gesture events. * Ditto for explicit `*Listener` only classes, make sure they're based on `EventListener` instead of something uselessly fancier. * Unless absolutely necessary, do not store references in class objects, ever; only values. Instead, always store references in instances, to avoid both sneaky inheritance issues, and sneaky GC pinning of stale references. * ReaderUI: Fix one such issue with its `active_widgets` array, with critical implications, as it essentially pinned *all* of ReaderUI's modules, including their reference to the `Document` instance (i.e., that was a big-ass leak). * Terminal: Make sure the shell is killed on plugin teardown. * InputText: Fix Home/End/Del physical keys to behave sensibly. * InputContainer/WidgetContainer: If necessary, compute self.dimen at paintTo time (previously, only InputContainers did, which might have had something to do with random widgets unconcerned about input using it as a baseclass instead of WidgetContainer...). * OverlapGroup: Compute self.dimen at *init* time, because for some reason it needs to do that, but do it directly in OverlapGroup instead of going through a weird WidgetContainer method that it was the sole user of. * ReaderCropping: Under no circumstances should a Document instance member (here, self.bbox) risk being `nil`ed! * Kobo: Minor code cleanups.
2025-12-13 20:36:53 +01:00 · 2022-10-06 02:14:48 +02:00
parent 7b9f02e1ac
commit fadee1f5dc
223 changed files with 849 additions and 985 deletions
--- a/2
+++ b/2
--- a/frontend/apps/filemanager/filemanager.lua
+++ b/frontend/apps/filemanager/filemanager.lua
@@ -44,6 +44,7 @@ local T = BaseUtil.template

 local FileManager = InputContainer:extend{
    title = _("KOReader"),
+    active_widgets = nil, -- array
    root_path = lfs.currentdir(),

    clipboard = nil, -- for single file operations
--- a/frontend/apps/filemanager/filemanagerbookinfo.lua
+++ b/frontend/apps/filemanager/filemanagerbookinfo.lua
@@ -7,15 +7,15 @@ local DocSettings = require("docsettings")
 local DocumentRegistry = require("document/documentregistry")
 local ImageViewer = require("ui/widget/imageviewer")
 local InfoMessage = require("ui/widget/infomessage")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local KeyValuePage = require("ui/widget/keyvaluepage")
 local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local filemanagerutil = require("apps/filemanager/filemanagerutil")
 local lfs = require("libs/libkoreader-lfs")
 local util = require("util")
 local _ = require("gettext")

-local BookInfo = InputContainer:extend{
+local BookInfo = WidgetContainer:extend{
    bookinfo_menu_title = _("Book information"),
 }

--- a/frontend/apps/filemanager/filemanagercollection.lua
+++ b/frontend/apps/filemanager/filemanagercollection.lua
@@ -3,17 +3,17 @@ local ButtonDialogTitle = require("ui/widget/buttondialogtitle")
 local Device = require("device")
 local FileManagerBookInfo = require("apps/filemanager/filemanagerbookinfo")
 local InfoMessage = require("ui/widget/infomessage")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local Menu = require("ui/widget/menu")
 local ReadCollection = require("readcollection")
 local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local Screen = require("device").screen
 local BaseUtil = require("ffi/util")
 local util = require("util")
 local _ = require("gettext")
 local T = BaseUtil.template

-local FileManagerCollection = InputContainer:extend{
+local FileManagerCollection = WidgetContainer:extend{
    coll_menu_title = _("Favorites"),
 }

--- a/frontend/apps/filemanager/filemanagerfilesearcher.lua
+++ b/frontend/apps/filemanager/filemanagerfilesearcher.lua
@@ -4,23 +4,23 @@ local CenterContainer = require("ui/widget/container/centercontainer")
 local DocumentRegistry = require("document/documentregistry")
 local FileChooser = require("ui/widget/filechooser")
 local InfoMessage = require("ui/widget/infomessage")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local InputDialog = require("ui/widget/inputdialog")
 local Menu = require("ui/widget/menu")
 local Size = require("ui/size")
 local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
+local BaseUtil = require("ffi/util")
 local Utf8Proc = require("ffi/utf8proc")
 local lfs = require("libs/libkoreader-lfs")
-local BaseUtil = require("ffi/util")
 local util = require("util")
 local _ = require("gettext")
 local Screen = require("device").screen
 local T = require("ffi/util").template

-local FileSearcher = InputContainer:new{
-    dirs = {},
-    files = {},
-    results = {},
+local FileSearcher = WidgetContainer:extend{
+    dirs = nil, -- table
+    files = nil, -- table
+    results = nil, -- table

    case_sensitive = false,
    include_subfolders = true,
@@ -32,6 +32,12 @@ local sys_folders = { -- do not search in sys_folders
    ["/sys"] = true,
 }

+function FileSearcher:init()
+    self.dirs = {}
+    self.files = {}
+    self.results = {}
+end
+
 function FileSearcher:readDir()
    local ReaderUI = require("apps/reader/readerui")
    local show_unsupported = G_reader_settings:isTrue("show_unsupported")
--- a/frontend/apps/filemanager/filemanagerhistory.lua
+++ b/frontend/apps/filemanager/filemanagerhistory.lua
@@ -4,9 +4,9 @@ local ConfirmBox = require("ui/widget/confirmbox")
 local DocSettings = require("docsettings")
 local FFIUtil = require("ffi/util")
 local FileManagerBookInfo = require("apps/filemanager/filemanagerbookinfo")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local Menu = require("ui/widget/menu")
 local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local Screen = require("device").screen
 local filemanagerutil = require("apps/filemanager/filemanagerutil")
 local lfs = require("libs/libkoreader-lfs")
@@ -14,7 +14,7 @@ local _ = require("gettext")
 local C_ = _.pgettext
 local T = FFIUtil.template

-local FileManagerHistory = InputContainer:extend{
+local FileManagerHistory = WidgetContainer:extend{
    hist_menu_title = _("History"),
 }

--- a/frontend/apps/filemanager/filemanagermenu.lua
+++ b/frontend/apps/filemanager/filemanagermenu.lua
@@ -19,7 +19,7 @@ local T = FFIUtil.template

 local FileManagerMenu = InputContainer:extend{
    tab_item_table = nil,
-    menu_items = {},
+    menu_items = nil, -- table, mandatory
    registered_widgets = nil,
 }

@@ -522,22 +522,20 @@ To:
            end,
        })
    end
-    if not Device.should_restrict_JIT then
-        local Blitbuffer = require("ffi/blitbuffer")
-        table.insert(self.menu_items.developer_options.sub_item_table, {
-            text = _("Disable C blitter"),
-            enabled_func = function()
-                return Blitbuffer.has_cblitbuffer
-            end,
-            checked_func = function()
-                return G_reader_settings:isTrue("dev_no_c_blitter")
-            end,
-            callback = function()
-                G_reader_settings:flipNilOrFalse("dev_no_c_blitter")
-                Blitbuffer:enableCBB(G_reader_settings:nilOrFalse("dev_no_c_blitter"))
-            end,
-        })
-    end
+    local Blitbuffer = require("ffi/blitbuffer")
+    table.insert(self.menu_items.developer_options.sub_item_table, {
+        text = _("Disable C blitter"),
+        enabled_func = function()
+            return Blitbuffer.has_cblitbuffer
+        end,
+        checked_func = function()
+            return G_reader_settings:isTrue("dev_no_c_blitter")
+        end,
+        callback = function()
+            G_reader_settings:flipNilOrFalse("dev_no_c_blitter")
+            Blitbuffer:enableCBB(G_reader_settings:nilOrFalse("dev_no_c_blitter"))
+        end,
+    })
    if Device:hasEinkScreen() and Device:canHWDither() then
        table.insert(self.menu_items.developer_options.sub_item_table, {
            text = _("Disable HW dithering"),
--- a/frontend/apps/filemanager/filemanagersetdefaults.lua
+++ b/frontend/apps/filemanager/filemanagersetdefaults.lua
@@ -21,11 +21,10 @@ local SetDefaultsWidget = CenterContainer:extend{
 }

 function SetDefaultsWidget:init()
-    -- We're a CenterContainer, so handle our own stuff first
+    -- This would usually be passed to the constructor, as CenterContainer's paintTo does *NOT* set/update self.dimen...
    self.dimen = Screen:getSize()
    -- Don't refresh the FM behind us. May leave stray bits of overflowed InputDialog behind in the popout border space.
    self.covers_fullscreen = true
-    CenterContainer.init(self)

    -- Then deal with our child widgets and our internal variables
    self.screen_width = Screen:getWidth()
--- a/frontend/apps/filemanager/filemanagershortcuts.lua
+++ b/frontend/apps/filemanager/filemanagershortcuts.lua
@@ -1,17 +1,17 @@
 local BD = require("ui/bidi")
 local ButtonDialog = require("ui/widget/buttondialog")
 local InfoMessage = require("ui/widget/infomessage")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local InputDialog = require("ui/widget/inputdialog")
 local Menu = require("ui/widget/menu")
 local Screen = require("device").screen
 local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local lfs = require("libs/libkoreader-lfs")
 local util = require("ffi/util")
 local _ = require("gettext")
 local T = util.template

-local FileManagerShortcuts = InputContainer:extend{
+local FileManagerShortcuts = WidgetContainer:extend{
    folder_shortcuts = G_reader_settings:readSetting("folder_shortcuts", {}),
 }

--- a/frontend/apps/reader/modules/readerback.lua
+++ b/frontend/apps/reader/modules/readerback.lua
@@ -13,8 +13,8 @@ local _ = require("gettext")
 -- additionally handles a location stack for each visited page or
 -- page view change (when scrolling in a same page)

-local ReaderBack = EventListener:new{
-    location_stack = {},
+local ReaderBack = EventListener:extend{
+    location_stack = nil, -- array
    -- a limit not intended to be a practical limit but just a failsafe
    max_stack = 5000,
 }
--- a/frontend/apps/reader/modules/readerbookmark.lua
+++ b/frontend/apps/reader/modules/readerbookmark.lua
@@ -31,7 +31,7 @@ local DISPLAY_PREFIX = {
    bookmark = "\u{F097}\u{2002}", -- "empty bookmark"
 }

-local ReaderBookmark = InputContainer:new{
+local ReaderBookmark = InputContainer:extend{
    bookmarks_items_per_page_default = 14,
    bookmarks = nil,
 }
--- a/frontend/apps/reader/modules/readerconfig.lua
+++ b/frontend/apps/reader/modules/readerconfig.lua
@@ -1,14 +1,13 @@
 local ConfigDialog = require("ui/widget/configdialog")
 local Device = require("device")
 local Event = require("ui/event")
-local Geom = require("ui/geometry")
 local InputContainer = require("ui/widget/container/inputcontainer")
 local UIManager = require("ui/uimanager")
 local CreOptions = require("ui/data/creoptions")
 local KoptOptions = require("ui/data/koptoptions")
 local _ = require("gettext")

-local ReaderConfig = InputContainer:new{
+local ReaderConfig = InputContainer:extend{
    last_panel_index = 1,
 }

@@ -20,7 +19,6 @@ function ReaderConfig:init()
    end
    self.configurable:loadDefaults(self.options)

-    if not self.dimen then self.dimen = Geom:new{} end
    if Device:hasKeys() then
        self.key_events = {
            ShowConfigMenu = { {{"Press","AA"}}, doc = "show config dialog" },
@@ -120,7 +118,6 @@ end

 function ReaderConfig:onShowConfigMenu()
    self.config_dialog = ConfigDialog:new{
-        dimen = self.dimen:copy(),
        document = self.document,
        ui = self.ui,
        configurable = self.configurable,
--- a/frontend/apps/reader/modules/readercoptlistener.lua
+++ b/frontend/apps/reader/modules/readercoptlistener.lua
@@ -8,7 +8,7 @@ local logger = require("logger")
 local T = require("ffi/util").template
 local _ = require("gettext")

-local ReaderCoptListener = EventListener:new{}
+local ReaderCoptListener = EventListener:extend{}

 local CRE_HEADER_DEFAULT_SIZE = 20

--- a/frontend/apps/reader/modules/readercropping.lua
+++ b/frontend/apps/reader/modules/readercropping.lua
@@ -5,15 +5,15 @@ local CenterContainer = require("ui/widget/container/centercontainer")
 local Event = require("ui/event")
 local FrameContainer = require("ui/widget/container/framecontainer")
 local Geom = require("ui/geometry")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local Math = require("optmath")
 local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local VerticalGroup = require("ui/widget/verticalgroup")
 local Device = require("device")
 local Screen = Device.screen
 local _ = require("gettext")

-local ReaderCropping = InputContainer:new{}
+local ReaderCropping = WidgetContainer:extend{}

 function ReaderCropping:onPageCrop(mode)
    self.ui:handleEvent(Event:new("CloseConfigMenu"))
@@ -171,7 +171,9 @@ function ReaderCropping:setZoomMode(mode)
 end

 function ReaderCropping:onReadSettings(config)
-    self.document.bbox = config:readSetting("bbox")
+    if config:has("bbox") then
+        self.document.bbox = config:readSetting("bbox")
+    end
 end

 function ReaderCropping:onSaveSettings()
--- a/frontend/apps/reader/modules/readerdevicestatus.lua
+++ b/frontend/apps/reader/modules/readerdevicestatus.lua
@@ -2,15 +2,15 @@ local ConfirmBox = require("ui/widget/confirmbox")
 local Device = require("device")
 local Event = require("ui/event")
 local InfoMessage = require("ui/widget/infomessage")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local SpinWidget = require("ui/widget/spinwidget")
 local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local powerd = Device:getPowerDevice()
 local _ = require("gettext")
 local C_ = _.pgettext
 local T = require("ffi/util").template

-local ReaderDeviceStatus = InputContainer:new{
+local ReaderDeviceStatus = WidgetContainer:extend{
    battery_confirm_box = nil,
    memory_confirm_box = nil,
 }
--- a/frontend/apps/reader/modules/readerdictionary.lua
+++ b/frontend/apps/reader/modules/readerdictionary.lua
@@ -6,7 +6,6 @@ local DictQuickLookup = require("ui/widget/dictquicklookup")
 local Event = require("ui/event")
 local Geom = require("ui/geometry")
 local InfoMessage = require("ui/widget/infomessage")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local InputDialog = require("ui/widget/inputdialog")
 local JSON = require("json")
 local KeyValuePage = require("ui/widget/keyvaluepage")
@@ -16,6 +15,7 @@ local NetworkMgr = require("ui/network/manager")
 local SortWidget = require("ui/widget/sortwidget")
 local Trapper = require("ui/trapper")
 local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local ffi = require("ffi")
 local C = ffi.C
 local ffiUtil  = require("ffi/util")
@@ -60,9 +60,9 @@ local function getIfosInDir(path)
    return ifos
 end

-local ReaderDictionary = InputContainer:new{
+local ReaderDictionary = WidgetContainer:extend{
    data_dir = nil,
-    dict_window_list = {},
+    dict_window_list = nil, -- array
    lookup_msg = _("Searching dictionary for:\n%1"),
 }

@@ -100,6 +100,7 @@ local function getDictionaryFixHtmlFunc(path)
 end

 function ReaderDictionary:init()
+    self.dict_window_list = {}
    self.disable_lookup_history = G_reader_settings:isTrue("disable_lookup_history")
    self.dicts_order = G_reader_settings:readSetting("dicts_order", {})
    self.dicts_disabled = G_reader_settings:readSetting("dicts_disabled", {})
@@ -156,7 +157,7 @@ function ReaderDictionary:init()
    self:updateSdcvDictNamesOptions()

    if not lookup_history then
-        lookup_history = LuaData:open(DataStorage:getSettingsDir() .. "/lookup_history.lua", { name = "LookupHistory" })
+        lookup_history = LuaData:open(DataStorage:getSettingsDir() .. "/lookup_history.lua", "LookupHistory")
    end
 end

--- a/frontend/apps/reader/modules/readerdogear.lua
+++ b/frontend/apps/reader/modules/readerdogear.lua
@@ -2,13 +2,13 @@ local BD = require("ui/bidi")
 local Device = require("device")
 local Geom = require("ui/geometry")
 local IconWidget = require("ui/widget/iconwidget")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local RightContainer = require("ui/widget/container/rightcontainer")
 local VerticalGroup = require("ui/widget/verticalgroup")
 local VerticalSpan = require("ui/widget/verticalspan")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local Screen = Device.screen

-local ReaderDogear = InputContainer:new{}
+local ReaderDogear = WidgetContainer:extend{}

 function ReaderDogear:init()
    -- This image could be scaled for DPI (with scale_for_dpi=true, scale_factor=0.7),
--- a/frontend/apps/reader/modules/readerflipping.lua
+++ b/frontend/apps/reader/modules/readerflipping.lua
@@ -1,10 +1,10 @@
 local Geom = require("ui/geometry")
 local IconWidget = require("ui/widget/iconwidget")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local LeftContainer = require("ui/widget/container/leftcontainer")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local Screen = require("device").screen

-local ReaderFlipping = InputContainer:new{
+local ReaderFlipping = WidgetContainer:extend{
    orig_reflow_mode = 0,
 }

--- a/frontend/apps/reader/modules/readerfont.lua
+++ b/frontend/apps/reader/modules/readerfont.lua
@@ -19,7 +19,7 @@ local _ = require("gettext")
 local C_ = _.pgettext
 local optionsutil = require("ui/data/optionsutil")

-local ReaderFont = InputContainer:new{
+local ReaderFont = InputContainer:extend{
    font_face = nil,
    font_size = nil,
    line_space_percent = nil,
--- a/frontend/apps/reader/modules/readerfooter.lua
+++ b/frontend/apps/reader/modules/readerfooter.lua
@@ -444,7 +444,7 @@ local ReaderFooter = WidgetContainer:extend{
    height = Screen:scaleBySize(G_defaults:readSetting("DMINIBAR_CONTAINER_HEIGHT")),
    horizontal_margin = Size.span.horizontal_default,
    bottom_padding = Size.padding.tiny,
-    settings = {},
+    settings = nil, -- table
    -- added to expose them to unit tests
    textGeneratorMap = footerTextGeneratorMap,
 }
--- a/frontend/apps/reader/modules/readergoto.lua
+++ b/frontend/apps/reader/modules/readergoto.lua
@@ -1,13 +1,12 @@
 local Event = require("ui/event")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local InputDialog = require("ui/widget/inputdialog")
 local SkimToWidget = require("ui/widget/skimtowidget")
 local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local _ = require("gettext")
 local T = require("ffi/util").template

-local ReaderGoto = InputContainer:new{
-}
+local ReaderGoto = WidgetContainer:extend{}

 function ReaderGoto:init()
    self.ui.menu:registerToMainMenu(self)
--- a/frontend/apps/reader/modules/readerhighlight.lua
+++ b/frontend/apps/reader/modules/readerhighlight.lua
@@ -20,8 +20,7 @@ local C_ = _.pgettext
 local T = require("ffi/util").template
 local Screen = Device.screen

-local ReaderHighlight = InputContainer:new{
-}
+local ReaderHighlight = InputContainer:extend{}

 local function inside_box(pos, box)
    if pos then
--- a/frontend/apps/reader/modules/readerhinting.lua
+++ b/frontend/apps/reader/modules/readerhinting.lua
@@ -2,10 +2,14 @@ local EventListener = require("ui/widget/eventlistener")

 local DHINTCOUNT = G_defaults:readSetting("DHINTCOUNT")

-local ReaderHinting = EventListener:new{
-    hinting_states = {}
+local ReaderHinting = EventListener:extend{
+    hinting_states = nil, -- array
 }

+function ReaderHinting:init()
+    self.hinting_states = {}
+end
+
 function ReaderHinting:onHintPage()
    if not self.view.hinting then return true end
    for i=1, DHINTCOUNT do
--- a/frontend/apps/reader/modules/readerkoptlistener.lua
+++ b/frontend/apps/reader/modules/readerkoptlistener.lua
@@ -4,7 +4,7 @@ local ReaderZooming = require("apps/reader/modules/readerzooming")
 local UIManager = require("ui/uimanager")
 local util = require("util")

-local ReaderKoptListener = EventListener:new{}
+local ReaderKoptListener = EventListener:extend{}

 function ReaderKoptListener:setZoomMode(zoom_mode)
    if self.document.configurable.text_wrap == 1 then
--- a/frontend/apps/reader/modules/readerlink.lua
+++ b/frontend/apps/reader/modules/readerlink.lua
@@ -21,8 +21,8 @@ local _ = require("gettext")
 local Screen = Device.screen
 local T = ffiutil.template

-local ReaderLink = InputContainer:new{
-    location_stack = {}
+local ReaderLink = InputContainer:extend{
+    location_stack = nil, -- table, per-instance
 }

 function ReaderLink:init()
@@ -154,7 +154,7 @@ function ReaderLink:addToMainMenu(menu_items)
    -- insert table to main reader menu
    menu_items.go_to_previous_location = {
        text = _("Go back to previous location"),
-        enabled_func = function() return #self.location_stack > 0 end,
+        enabled_func = function() return self.location_stack and #self.location_stack > 0 end,
        callback = function() self:onGoBackLink() end,
        hold_callback = function(touchmenu_instance)
            UIManager:show(ConfirmBox:new{
--- a/frontend/apps/reader/modules/readermenu.lua
+++ b/frontend/apps/reader/modules/readermenu.lua
@@ -13,10 +13,10 @@ local Screen = Device.screen
 local _ = require("gettext")
 local T = require("ffi/util").template

-local ReaderMenu = InputContainer:new{
+local ReaderMenu = InputContainer:extend{
    tab_item_table = nil,
-    menu_items = {},
-    registered_widgets = {},
+    menu_items = nil, -- table, mandatory
+    registered_widgets = nil, -- array
 }

 function ReaderMenu:init()
--- a/frontend/apps/reader/modules/readerpagemap.lua
+++ b/frontend/apps/reader/modules/readerpagemap.lua
@@ -6,18 +6,18 @@ local Font = require("ui/font")
 local FrameContainer = require("ui/widget/container/framecontainer")
 local Geom = require("ui/geometry")
 local GestureRange = require("ui/gesturerange")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local Menu = require("ui/widget/menu")
 local MultiConfirmBox = require("ui/widget/multiconfirmbox")
 local OverlapGroup = require("ui/widget/overlapgroup")
 local TextBoxWidget = require("ui/widget/textboxwidget")
 local TextWidget = require("ui/widget/textwidget")
 local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local Screen = Device.screen
 local T = require("ffi/util").template
 local _ = require("gettext")

-local ReaderPageMap = InputContainer:new{
+local ReaderPageMap = WidgetContainer:extend{
    label_font_face = "ffont",
    label_default_font_size = 14,
    -- Black so it's readable (and non-gray-flashing on GloHD)
--- a/frontend/apps/reader/modules/readerpaging.lua
+++ b/frontend/apps/reader/modules/readerpaging.lua
@@ -27,7 +27,7 @@ local function copyPageState(page_state)
 end


-local ReaderPaging = InputContainer:new{
+local ReaderPaging = InputContainer:extend{
    pan_rate = 30,  -- default 30 ops, will be adjusted in readerui
    current_page = 0,
    number_of_pages = 0,
@@ -37,7 +37,7 @@ local ReaderPaging = InputContainer:new{

    page_flipping_mode = false,
    bookmark_flipping_mode = false,
-    flip_steps = {0,1,2,5,10,20,50,100},
+    flip_steps = {0, 1, 2, 5, 10, 20, 50, 100},
 }

 function ReaderPaging:init()
--- a/frontend/apps/reader/modules/readerpanning.lua
+++ b/frontend/apps/reader/modules/readerpanning.lua
@@ -2,7 +2,7 @@ local InputContainer = require("ui/widget/container/inputcontainer")
 local Device = require("device")
 local _ = require("gettext")

-local ReaderPanning = InputContainer:new{
+local ReaderPanning = InputContainer:extend{
    -- defaults
    panning_steps = {
        normal = 50,
--- a/frontend/apps/reader/modules/readerrolling.lua
+++ b/frontend/apps/reader/modules/readerrolling.lua
@@ -39,12 +39,12 @@ local band = bit.band
    it in explicit page turning. And use that xpointer for non-page-turning
    rendering.
 --]]
-local ReaderRolling = InputContainer:new{
+local ReaderRolling = InputContainer:extend{
    pan_rate = 30,  -- default 30 ops, will be adjusted in readerui
    rendering_hash = 0,
    current_pos = 0,
    -- only used for page view mode
-    current_page= nil,
+    current_page = nil,
    xpointer = nil,
    panning_steps = ReaderPanning.panning_steps,
    cre_top_bar_enabled = false,
--- a/frontend/apps/reader/modules/readerrotation.lua
+++ b/frontend/apps/reader/modules/readerrotation.lua
@@ -3,8 +3,8 @@ local Device = require("device")
 local Event = require("ui/event")
 local _ = require("gettext")

-local ReaderRotation = InputContainer:new{
-    current_rotation = 0
+local ReaderRotation = InputContainer:extend{
+    current_rotation = 0,
 }

 function ReaderRotation:init()
--- a/frontend/apps/reader/modules/readerscrolling.lua
+++ b/frontend/apps/reader/modules/readerscrolling.lua
@@ -1,7 +1,7 @@
 local Device = require("device")
 local Event = require("ui/event")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local logger = require("logger")
 local time = require("ui/time")
 local _ = require("gettext")
@@ -16,7 +16,7 @@ local SCROLL_METHOD_CLASSIC = "classic"
 local SCROLL_METHOD_TURBO = "turbo"
 local SCROLL_METHOD_ON_RELEASE = "on_release"

-local ReaderScrolling = InputContainer:new{
+local ReaderScrolling = WidgetContainer:extend{
    -- Available scrolling methods (make them available to other reader modules)
    SCROLL_METHOD_CLASSIC = SCROLL_METHOD_CLASSIC,
    SCROLL_METHOD_TURBO = SCROLL_METHOD_TURBO,
@@ -221,9 +221,6 @@ function ReaderScrolling:applyScrollSettings()
 end

 function ReaderScrolling:setupTouchZones()
-    self.ges_events = {}
-    self.onGesture = nil
-
    local zones = {
        {
            id = "inertial_scrolling_touch",
--- a/frontend/apps/reader/modules/readersearch.lua
+++ b/frontend/apps/reader/modules/readersearch.lua
@@ -3,10 +3,10 @@ local ButtonDialog = require("ui/widget/buttondialog")
 local CheckButton = require("ui/widget/checkbutton")
 local Device = require("device")
 local InfoMessage = require("ui/widget/infomessage")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local InputDialog = require("ui/widget/inputdialog")
 local Notification = require("ui/widget/notification")
 local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local logger = require("logger")
 local _ = require("gettext")
 local Screen = Device.screen
@@ -14,7 +14,7 @@ local T = require("ffi/util").template

 local DGENERIC_ICON_SIZE = G_defaults:readSetting("DGENERIC_ICON_SIZE")

-local ReaderSearch = InputContainer:new{
+local ReaderSearch = WidgetContainer:extend{
    direction = 0, -- 0 for search forward, 1 for search backward
    case_insensitive = true, -- default to case insensitive

--- a/frontend/apps/reader/modules/readerstatus.lua
+++ b/frontend/apps/reader/modules/readerstatus.lua
@@ -4,22 +4,16 @@ local ButtonDialogTitle = require("ui/widget/buttondialogtitle")
 local Device = require("device")
 local Event = require("ui/event")
 local InfoMessage = require("ui/widget/infomessage")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local util = require("util")
 local _ = require("gettext")
 local T = require("ffi/util").template

-local ReaderStatus = InputContainer:new {
+local ReaderStatus = WidgetContainer:extend{
    document = nil,
-    summary = {
-        rating = 0,
-        note = nil,
-        status = "",
-        modified = "",
-    },
    enabled = true,
-    total_pages = 0
+    total_pages = 0,
 }

 function ReaderStatus:init()
--- a/frontend/apps/reader/modules/readerstyletweak.lua
+++ b/frontend/apps/reader/modules/readerstyletweak.lua
@@ -19,6 +19,7 @@ local TextBoxWidget = require("ui/widget/textboxwidget")
 local UIManager = require("ui/uimanager")
 local VerticalGroup = require("ui/widget/verticalgroup")
 local VerticalSpan = require("ui/widget/verticalspan")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local lfs = require("libs/libkoreader-lfs")
 local logger = require("logger")
 local util = require("util")
@@ -27,7 +28,7 @@ local Screen = Device.screen
 local T = require("ffi/util").template

 -- Simple widget for showing tweak info
-local TweakInfoWidget = InputContainer:new{
+local TweakInfoWidget = InputContainer:extend{
    tweak = nil,
    is_global_default = nil,
    toggle_global_default_callback = function() end,
@@ -226,7 +227,7 @@ end

 -- Reader component for managing tweaks. The aggregated css_text
 -- is actually requested from us and applied by ReaderTypeset
-local ReaderStyleTweak = InputContainer:new{
+local ReaderStyleTweak = WidgetContainer:extend{
    tweaks_by_id = nil,
    tweaks_table = nil, -- sub-menu items
    nb_enabled_tweaks = 0, -- for use by main menu item
--- a/frontend/apps/reader/modules/readerthumbnail.lua
+++ b/frontend/apps/reader/modules/readerthumbnail.lua
@@ -2,11 +2,11 @@ local Blitbuffer = require("ffi/blitbuffer")
 local Cache = require("cache")
 local Device = require("device")
 local Geom = require("ui/geometry")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local Persist = require("persist")
 local RenderImage = require("ui/renderimage")
 local TileCacheItem = require("document/tilecacheitem")
 local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local Screen = Device.screen
 local ffiutil = require("ffi/util")
 local logger = require("logger")
@@ -18,7 +18,7 @@ local _ = require("gettext")
 -- It handles launching via the menu or Dispatcher/Gestures two fullscreen
 -- widgets related to showing pages and thumbnails that will make use of
 -- its services: BookMap and PageBrowser.
-local ReaderThumbnail = InputContainer:new{}
+local ReaderThumbnail = WidgetContainer:extend{}

 function ReaderThumbnail:init()
    if not Device:isTouchDevice() then
--- a/frontend/apps/reader/modules/readertoc.lua
+++ b/frontend/apps/reader/modules/readertoc.lua
@@ -20,15 +20,15 @@ local N_ = _.ngettext
 local Screen = Device.screen
 local T = require("ffi/util").template

-local ReaderToc = InputContainer:new{
+local ReaderToc = InputContainer:extend{
    toc = nil,
    toc_depth = nil,
    ticks = nil,
    ticks_flattened = nil,
    ticks_flattened_filtered = nil,
-    collapsed_toc = {},
+    collapsed_toc = nil, -- table
    collapse_depth = 2,
-    expanded_nodes = {},
+    expanded_nodes = nil, -- table
    toc_menu_title = _("Table of contents"),
    alt_toc_menu_title = _("Table of contents *"),
    toc_items_per_page_default = 14,
--- a/frontend/apps/reader/modules/readertypeset.lua
+++ b/frontend/apps/reader/modules/readertypeset.lua
@@ -2,10 +2,10 @@ local BD = require("ui/bidi")
 local ConfirmBox = require("ui/widget/confirmbox")
 local Event = require("ui/event")
 local InfoMessage = require("ui/widget/infomessage")
-local InputContainer = require("ui/widget/container/inputcontainer")
-local UIManager = require("ui/uimanager")
 local Math = require("optmath")
 local Notification = require("ui/widget/notification")
+local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local lfs = require("libs/libkoreader-lfs")
 local optionsutil = require("ui/data/optionsutil")
 local _ = require("gettext")
@@ -13,7 +13,7 @@ local C_ = _.pgettext
 local Screen = require("device").screen
 local T = require("ffi/util").template

-local ReaderTypeset = InputContainer:new{
+local ReaderTypeset = WidgetContainer:extend{
    -- @translators This is style in the sense meant by CSS (cascading style sheets), relating to the layout and presentation of the document. See <https://en.wikipedia.org/wiki/CSS> for more information.
    css_menu_title = C_("CSS", "Style"),
    css = nil,
--- a/frontend/apps/reader/modules/readertypography.lua
+++ b/frontend/apps/reader/modules/readertypography.lua
@@ -2,9 +2,9 @@ local BD = require("ui/bidi")
 local Device = require("device")
 local Event = require("ui/event")
 local InfoMessage = require("ui/widget/infomessage")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local MultiConfirmBox = require("ui/widget/multiconfirmbox")
 local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local logger = require("logger")
 local util = require("util")
 local _ = require("gettext")
@@ -12,7 +12,7 @@ local C_ = _.pgettext
 local T = require("ffi/util").template
 local Screen = Device.screen

-local ReaderTypography = InputContainer:new{}
+local ReaderTypography = WidgetContainer:extend{}

 -- This is used to migrate old hyph settings, and to show the currently
 -- used hyph dict language in the hyphenation menu.
--- a/frontend/apps/reader/modules/readeruserhyph.lua
+++ b/frontend/apps/reader/modules/readeruserhyph.lua
@@ -16,7 +16,7 @@ local T = require("ffi/util").template
 -- and some `if NORM then` branches can be simplified.
 local NORM = false

-local ReaderUserHyph = WidgetContainer:new{
+local ReaderUserHyph = WidgetContainer:extend{
    -- return values from setUserHyphenationDict (crengine's UserHyphDict::init())
    USER_DICT_RELOAD = 0,
    USER_DICT_NOCHANGE = 1,
--- a/frontend/apps/reader/modules/readerview.lua
+++ b/frontend/apps/reader/modules/readerview.lua
@@ -28,28 +28,13 @@ local T = require("ffi/util").template

 local ReaderView = OverlapGroup:extend{
    document = nil,
+    view_modules = nil, -- array

    -- single page state
-    state = {
-        page = nil,
-        pos = 0,
-        zoom = 1.0,
-        rotation = 0,
-        gamma = 1.0,
-        offset = nil,
-        bbox = nil,
-    },
+    state = nil, -- table
    outer_page_color = Blitbuffer.gray(G_defaults:readSetting("DOUTER_PAGE_COLOR") / 15),
    -- highlight with "lighten" or "underscore" or "strikeout" or "invert"
-    highlight = {
-        lighten_factor = G_reader_settings:readSetting("highlight_lighten_factor", 0.2),
-        note_mark = G_reader_settings:readSetting("highlight_note_marker"),
-        temp_drawer = "invert",
-        temp = {},
-        saved_drawer = "lighten",
-        saved = {},
-        indicator = nil, -- geom: non-touch highlight position indicator: {x = 50, y=50}
-    },
+    highlight = nil, -- table
    highlight_visible = true,
    note_mark_line_w = 3, -- side line thickness
    note_mark_sign = nil,
@@ -58,12 +43,9 @@ local ReaderView = OverlapGroup:extend{
    -- PDF/DjVu continuous paging
    page_scroll = nil,
    page_bgcolor = Blitbuffer.gray(G_defaults:readSetting("DBACKGROUND_COLOR") / 15),
-    page_states = {},
+    page_states = nil, -- table
    -- properties of the gap drawn between each page in scroll mode:
-    page_gap = {
-        -- color (0 = white, 8 = gray, 15 = black)
-        color = Blitbuffer.gray((G_reader_settings:readSetting("page_gap_color") or 8) / 15),
-    },
+    page_gap = nil, -- table
    -- DjVu page rendering mode (used in djvu.c:drawPage())
    render_mode = G_defaults:readSetting("DRENDER_MODE"), -- default to COLOR
    -- Crengine view mode
@@ -91,10 +73,30 @@ local ReaderView = OverlapGroup:extend{

 function ReaderView:init()
    self.view_modules = {}
-    -- fix recalculate from close document pageno
-    self.state.page = nil

-    -- Reset the various areas across documents
+    self.state = {
+        page = nil,
+        pos = 0,
+        zoom = 1.0,
+        rotation = 0,
+        gamma = 1.0,
+        offset = nil,
+        bbox = nil,
+    }
+    self.highlight = {
+        lighten_factor = G_reader_settings:readSetting("highlight_lighten_factor", 0.2),
+        note_mark = G_reader_settings:readSetting("highlight_note_marker"),
+        temp_drawer = "invert",
+        temp = {},
+        saved_drawer = "lighten",
+        saved = {},
+        indicator = nil, -- geom: non-touch highlight position indicator: {x = 50, y=50}
+    }
+    self.page_states = {}
+    self.page_gap = {
+        -- color (0 = white, 8 = gray, 15 = black)
+        color = Blitbuffer.gray((G_reader_settings:readSetting("page_gap_color") or 8) / 15),
+    }
    self.visible_area = Geom:new{x = 0, y = 0, w = 0, h = 0}
    self.page_area = Geom:new{x = 0, y = 0, w = 0, h = 0}
    self.dim_area = Geom:new{x = 0, y = 0, w = 0, h = 0}
@@ -103,6 +105,9 @@ function ReaderView:init()
    self.emitHintPageEvent = function()
        self.ui:handleEvent(Event:new("HintPage", self.hinting))
    end
+
+    -- We've subclassed OverlapGroup, go through its init, because it does some funky stuff with self.dimen...
+    OverlapGroup.init(self)
 end

 function ReaderView:addWidgets()
@@ -1071,8 +1076,7 @@ function ReaderView:getRenderModeMenuTable()
 end

 function ReaderView:onCloseDocument()
-    self.hinting = false
-    -- stop any in fly HintPage event
+    -- stop any pending HintPage event
    UIManager:unschedule(self.emitHintPageEvent)
 end

--- a/frontend/apps/reader/modules/readerwikipedia.lua
+++ b/frontend/apps/reader/modules/readerwikipedia.lua
@@ -31,7 +31,7 @@ function ReaderWikipedia:init()
    self.wiki_languages = {}
    self.ui.menu:registerToMainMenu(self)
    if not wikipedia_history then
-        wikipedia_history = LuaData:open(DataStorage:getSettingsDir() .. "/wikipedia_history.lua", { name = "WikipediaHistory" })
+        wikipedia_history = LuaData:open(DataStorage:getSettingsDir() .. "/wikipedia_history.lua", "WikipediaHistory")
    end
 end

--- a/frontend/apps/reader/modules/readerzooming.lua
+++ b/frontend/apps/reader/modules/readerzooming.lua
@@ -14,9 +14,9 @@ local Input = Device.input
 local Screen = Device.screen
 local T = require("ffi/util").template

-local ReaderZooming = InputContainer:new{
+local ReaderZooming = InputContainer:extend{
    zoom = 1.0,
-    available_zoom_modes = {
+    available_zoom_modes = { -- const
        "page",
        "pagewidth",
        "pageheight",
@@ -27,26 +27,26 @@ local ReaderZooming = InputContainer:new{
        "rows",
        "manual",
    },
-    zoom_genus_to_mode = {
+    zoom_genus_to_mode = { -- const
        [4] = "page",
        [3] = "content",
        [2] = "columns",
        [1] = "rows",
        [0] = "manual",
    },
-    zoom_mode_to_genus = {
+    zoom_mode_to_genus = { -- const
        page    = 4,
        content = 3,
        columns = 2,
        rows    = 1,
        manual  = 0,
    },
-    zoom_type_to_mode = {
+    zoom_type_to_mode = { -- const
        [2] = "",
        [1] = "width",
        [0] = "height",
    },
-    zoom_mode_to_type = {
+    zoom_mode_to_type = { -- const
        [""]   = 2,
        width  = 1,
        height = 0,
@@ -58,7 +58,7 @@ local ReaderZooming = InputContainer:new{
    -- with overlap of zoom_overlap_h % (horizontally)
    -- and zoom_overlap_v % (vertically).
    kopt_zoom_factor = 1.5,
-    zoom_pan_settings = {
+    zoom_pan_settings = { -- const
        "kopt_zoom_factor",
        "zoom_overlap_h",
        "zoom_overlap_v",
@@ -71,7 +71,7 @@ local ReaderZooming = InputContainer:new{
    zoom_direction_vertical = nil, -- true for column mode
    current_page = 1,
    rotation = 0,
-    paged_modes = {
+    paged_modes = { -- const
        page = _("Zoom to fit page works best with page view."),
        pageheight = _("Zoom to fit page height works best with page view."),
        contentheight = _("Zoom to fit content height works best with page view."),
--- a/frontend/apps/reader/readerui.lua
+++ b/frontend/apps/reader/readerui.lua
@@ -66,9 +66,9 @@ local _ = require("gettext")
 local Screen = require("device").screen
 local T = ffiUtil.template

-local ReaderUI = InputContainer:new{
+local ReaderUI = InputContainer:extend{
    name = "ReaderUI",
-    active_widgets = {},
+    active_widgets = nil, -- array

    -- if we have a parent container, it must be referenced for now
    dialog = nil,
@@ -104,6 +104,8 @@ function ReaderUI:registerPostReadyCallback(callback)
 end

 function ReaderUI:init()
+    self.active_widgets = {}
+
    -- cap screen refresh on pan to 2 refreshes per second
    local pan_rate = Screen.low_pan_rate and 2.0 or 30.0

--- a/frontend/cache.lua
+++ b/frontend/cache.lua
@@ -8,11 +8,6 @@ local lru = require("ffi/lru")
 local md5 = require("ffi/sha2").md5
 local util = require("util")

-local CanvasContext = require("document/canvascontext")
-if CanvasContext.should_restrict_JIT then
-    jit.off(true, true)
-end
-
 local Cache = {
    -- Cache configuration:
    -- Max storage space, in bytes...
--- a/frontend/cacheitem.lua
+++ b/frontend/cacheitem.lua
@@ -9,12 +9,15 @@ local CacheItem = {
 ---       and the most common items we cache are Geom-like tables (i.e., 4 key-value pairs).
 ---       That's generally a low estimation, especially for larger tables, where memory allocation trickery may be happening.

-function CacheItem:new(o)
+function CacheItem:extend(o)
    o = o or {}
    setmetatable(o, self)
    self.__index = self
    return o
 end
+-- NOTE: There's no object-specific initialization, the entirety of the new data *is* the table we pass to new.
+--       We only keep the distinction as a matter of semantics, to differentiate class declarations from object instantiations.
+CacheItem.new = CacheItem.extend

 -- Called on eviction.
 -- We generally use it to free C/FFI resources *immediately* (as opposed to relying on our Userdata/FFI finalizers to do it "later" on GC).
--- a/frontend/device/android/device.lua
+++ b/frontend/device/android/device.lua
@@ -67,7 +67,7 @@ local external = require("device/thirdparty"):new{
    end,
 }

-local Device = Generic:new{
+local Device = Generic:extend{
    isAndroid = yes,
    model = android.prop.product,
    hasKeys = yes,
@@ -111,21 +111,6 @@ local Device = Generic:new{
            android.dictLookup(text, app, action)
        end
    end,
-
-    -- Android is very finicky, and the LuaJIT allocator has a tremendously hard time getting the system
-    -- to allocate memory for it in the very specific memory range it requires to store generated code (mcode).
-    -- Failure to do so at runtime (mcode_alloc) will *tank* performance
-    -- (much worse than if the JIT were simply disabled).
-    -- The first line of defense is left to android-luajit-launcher,
-    -- which will try to grab the full mcode region in one go right at startup.
-    -- The second line of defense is *this* flag, which disables the JIT in a few code-hungry modules,
-    -- but not necessarily performance critical ones, to hopefully limit the amount of mcode memory
-    -- required for those modules where it *really* matters (e.g., ffi/blitbuffer.lua).
-    -- This is also why we try to actually avoid entering actual loops in the Lua blitter on Android,
-    -- and instead attempt to do most of everything via the C implementation.
-    -- NOTE: Since https://github.com/koreader/android-luajit-launcher/pull/283, we've patched LuaJIT
-    --       to ensure that the initial mcode alloc works, and sticks around, which is why this is no longer enabled.
-    should_restrict_JIT = false,
 }

 function Device:init()
--- a/frontend/device/cervantes/device.lua
+++ b/frontend/device/cervantes/device.lua
@@ -34,7 +34,7 @@ local function isMassStorageSupported()
    return true
 end

-local Cervantes = Generic:new{
+local Cervantes = Generic:extend{
    model = "Cervantes",
    isCervantes = yes,
    isAlwaysPortrait = yes,
@@ -65,33 +65,33 @@ local Cervantes = Generic:new{
    canHWInvert = yes,
 }
 -- Cervantes Touch
-local CervantesTouch = Cervantes:new{
+local CervantesTouch = Cervantes:extend{
    model = "CervantesTouch",
    display_dpi = 167,
    hasFrontlight = no,
    hasMultitouch = no,
 }
 -- Cervantes TouchLight / Fnac Touch Plus
-local CervantesTouchLight = Cervantes:new{
+local CervantesTouchLight = Cervantes:extend{
    model = "CervantesTouchLight",
    display_dpi = 167,
    hasMultitouch = no,
 }
 -- Cervantes 2013 / Fnac Touch Light
-local Cervantes2013 = Cervantes:new{
+local Cervantes2013 = Cervantes:extend{
    model = "Cervantes2013",
    display_dpi = 212,
    hasMultitouch = no,
    --- @fixme: Possibly requires canHWInvert = no, as it seems to be based on a similar board as the Kobo Aura...
 }
 -- Cervantes 3 / Fnac Touch Light 2
-local Cervantes3 = Cervantes:new{
+local Cervantes3 = Cervantes:extend{
    model = "Cervantes3",
    display_dpi = 300,
    hasMultitouch = no,
 }
 -- Cervantes 4
-local Cervantes4 = Cervantes:new{
+local Cervantes4 = Cervantes:extend{
    model = "Cervantes4",
    display_dpi = 300,
    hasNaturalLight = yes,
--- a/frontend/device/devicelistener.lua
+++ b/frontend/device/devicelistener.lua
@@ -1,6 +1,6 @@
 local Device = require("device")
 local Event = require("ui/event")
-local InputContainer = require("ui/widget/container/inputcontainer")
+local EventListener = require("ui/widget/eventlistener")
 local Notification = require("ui/widget/notification")
 local Screen = Device.screen
 local UIManager = require("ui/uimanager")
@@ -8,7 +8,7 @@ local bit = require("bit")
 local _ = require("gettext")
 local T = require("ffi/util").template

-local DeviceListener = InputContainer:new{}
+local DeviceListener = EventListener:extend{}

 local function _setSetting(name)
    G_reader_settings:makeTrue(name)
--- a/frontend/device/dummy/device.lua
+++ b/frontend/device/dummy/device.lua
@@ -4,7 +4,7 @@ local logger = require("logger")
 local function yes() return true end
 local function no() return false end

-local Device = Generic:new{
+local Device = Generic:extend{
    model = "dummy",
    hasKeyboard = no,
    hasKeys = no,
--- a/frontend/device/generic/device.lua
+++ b/frontend/device/generic/device.lua
@@ -20,7 +20,6 @@ local Device = {
    charging_mode = false,
    survive_screen_saver = false,
    is_cover_closed = false,
-    should_restrict_JIT = false,
    model = nil,
    powerd = nil,
    screen = nil,
@@ -130,7 +129,7 @@ local Device = {
    canExternalDictLookup = no,
 }

-function Device:new(o)
+function Device:extend(o)
    o = o or {}
    setmetatable(o, self)
    self.__index = self
@@ -159,7 +158,6 @@ function Device:invertButtons()
 end

 function Device:init()
-    assert(self ~= nil)
    if not self.screen then
        error("screen/framebuffer must be implemented")
    end
--- a/frontend/device/generic/powerd.lua
+++ b/frontend/device/generic/powerd.lua
@@ -73,12 +73,10 @@ function BasePowerD:beforeSuspend() end
 function BasePowerD:afterResume() end

 function BasePowerD:isFrontlightOn()
-    assert(self ~= nil)
    return self.is_fl_on
 end

 function BasePowerD:_decideFrontlightState()
-    assert(self ~= nil)
    assert(self.device:hasFrontlight())
    self.is_fl_on = self:isFrontlightOnHW()
 end
@@ -88,7 +86,6 @@ function BasePowerD:isFrontlightOff()
 end

 function BasePowerD:frontlightIntensity()
-    assert(self ~= nil)
    if not self.device:hasFrontlight() then return 0 end
    if self:isFrontlightOff() then return 0 end
    --- @note: We assume that nothing other than us will set the frontlight level,
@@ -98,7 +95,6 @@ function BasePowerD:frontlightIntensity()
 end

 function BasePowerD:toggleFrontlight()
-    assert(self ~= nil)
    if not self.device:hasFrontlight() then return false end
    if self:isFrontlightOn() then
        return self:turnOffFrontlight()
@@ -108,7 +104,6 @@ function BasePowerD:toggleFrontlight()
 end

 function BasePowerD:turnOffFrontlight()
-    assert(self ~= nil)
    if not self.device:hasFrontlight() then return end
    if self:isFrontlightOff() then return false end
    self:turnOffFrontlightHW()
@@ -118,7 +113,6 @@ function BasePowerD:turnOffFrontlight()
 end

 function BasePowerD:turnOnFrontlight()
-    assert(self ~= nil)
    if not self.device:hasFrontlight() then return end
    if self:isFrontlightOn() then return false end
    if self.fl_intensity == self.fl_min then return false end  --- @fixme what the hell?
@@ -129,7 +123,6 @@ function BasePowerD:turnOnFrontlight()
 end

 function BasePowerD:frontlightWarmth()
-    assert(self ~= nil)
    if not self.device:hasNaturalLight() then
        return 0
    end
--- a/frontend/device/gesturedetector.lua
+++ b/frontend/device/gesturedetector.lua
@@ -63,6 +63,7 @@ local TWO_FINGER_TAP_DURATION_MS = 300
 local HOLD_INTERVAL_MS = 500
 local SWIPE_INTERVAL_MS = 900

+-- This is used as a singleton by Input (itself used as a singleton).
 local GestureDetector = {
    -- must be initialized with the Input singleton class
    input = nil,
@@ -73,7 +74,7 @@ local GestureDetector = {
    HOLD_INTERVAL_MS = HOLD_INTERVAL_MS,
    SWIPE_INTERVAL_MS = SWIPE_INTERVAL_MS,
    -- pinch/spread direction table
-    DIRECTION_TABLE = {
+    DIRECTION_TABLE = { -- const
        east = "horizontal",
        west = "horizontal",
        north = "vertical",
--- a/frontend/device/kindle/device.lua
+++ b/frontend/device/kindle/device.lua
@@ -141,7 +141,7 @@ local function frameworkStopped()
    end
 end

-local Kindle = Generic:new{
+local Kindle = Generic:extend{
    model = "Kindle",
    isKindle = yes,
    -- NOTE: We can cheat by adding a platform-specific entry here, because the only code that will check for this is here.
@@ -411,7 +411,7 @@ function Kindle:ambientBrightnessLevel()
    return 4
 end

-local Kindle2 = Kindle:new{
+local Kindle2 = Kindle:extend{
    model = "Kindle2",
    isREAGL = no,
    hasKeyboard = yes,
@@ -424,7 +424,7 @@ local Kindle2 = Kindle:new{
    supportsScreensaver = yes, -- The first ad-supported device was the K3
 }

-local KindleDXG = Kindle:new{
+local KindleDXG = Kindle:extend{
    model = "KindleDXG",
    isREAGL = no,
    hasKeyboard = yes,
@@ -437,7 +437,7 @@ local KindleDXG = Kindle:new{
    supportsScreensaver = yes, -- The first ad-supported device was the K3
 }

-local Kindle3 = Kindle:new{
+local Kindle3 = Kindle:extend{
    model = "Kindle3",
    isREAGL = no,
    hasKeyboard = yes,
@@ -449,7 +449,7 @@ local Kindle3 = Kindle:new{
    isSpecialOffers = hasSpecialOffers(),
 }

-local Kindle4 = Kindle:new{
+local Kindle4 = Kindle:extend{
    model = "Kindle4",
    isREAGL = no,
    hasKeys = yes,
@@ -461,7 +461,7 @@ local Kindle4 = Kindle:new{
    isSpecialOffers = hasSpecialOffers(),
 }

-local KindleTouch = Kindle:new{
+local KindleTouch = Kindle:extend{
    model = "KindleTouch",
    isREAGL = no,
    isTouchDevice = yes,
@@ -469,7 +469,7 @@ local KindleTouch = Kindle:new{
    touch_dev = "/dev/input/event3",
 }

-local KindlePaperWhite = Kindle:new{
+local KindlePaperWhite = Kindle:extend{
    model = "KindlePaperWhite",
    isREAGL = no,
    isTouchDevice = yes,
@@ -479,7 +479,7 @@ local KindlePaperWhite = Kindle:new{
    touch_dev = "/dev/input/event0",
 }

-local KindlePaperWhite2 = Kindle:new{
+local KindlePaperWhite2 = Kindle:extend{
    model = "KindlePaperWhite2",
    isTouchDevice = yes,
    hasFrontlight = yes,
@@ -488,13 +488,13 @@ local KindlePaperWhite2 = Kindle:new{
    touch_dev = "/dev/input/event1",
 }

-local KindleBasic = Kindle:new{
+local KindleBasic = Kindle:extend{
    model = "KindleBasic",
    isTouchDevice = yes,
    touch_dev = "/dev/input/event1",
 }

-local KindleVoyage = Kindle:new{
+local KindleVoyage = Kindle:extend{
    model = "KindleVoyage",
    isTouchDevice = yes,
    hasFrontlight = yes,
@@ -504,7 +504,7 @@ local KindleVoyage = Kindle:new{
    touch_dev = "/dev/input/event1",
 }

-local KindlePaperWhite3 = Kindle:new{
+local KindlePaperWhite3 = Kindle:extend{
    model = "KindlePaperWhite3",
    isTouchDevice = yes,
    hasFrontlight = yes,
@@ -513,7 +513,7 @@ local KindlePaperWhite3 = Kindle:new{
    touch_dev = "/dev/input/event1",
 }

-local KindleOasis = Kindle:new{
+local KindleOasis = Kindle:extend{
    model = "KindleOasis",
    isTouchDevice = yes,
    hasFrontlight = yes,
@@ -529,7 +529,7 @@ local KindleOasis = Kindle:new{
    touch_dev = "/dev/input/by-path/platform-imx-i2c.1-event",
 }

-local KindleOasis2 = Kindle:new{
+local KindleOasis2 = Kindle:extend{
    model = "KindleOasis2",
    isZelda = yes,
    isTouchDevice = yes,
@@ -540,7 +540,7 @@ local KindleOasis2 = Kindle:new{
    touch_dev = "/dev/input/by-path/platform-30a30000.i2c-event",
 }

-local KindleOasis3 = Kindle:new{
+local KindleOasis3 = Kindle:extend{
    model = "KindleOasis3",
    isZelda = yes,
    isTouchDevice = yes,
@@ -553,13 +553,13 @@ local KindleOasis3 = Kindle:new{
    touch_dev = "/dev/input/by-path/platform-30a30000.i2c-event",
 }

-local KindleBasic2 = Kindle:new{
+local KindleBasic2 = Kindle:extend{
    model = "KindleBasic2",
    isTouchDevice = yes,
    touch_dev = "/dev/input/event0",
 }

-local KindlePaperWhite4 = Kindle:new{
+local KindlePaperWhite4 = Kindle:extend{
    model = "KindlePaperWhite4",
    isRex = yes,
    isTouchDevice = yes,
@@ -571,7 +571,7 @@ local KindlePaperWhite4 = Kindle:new{
    touch_dev = "/dev/input/event2",
 }

-local KindleBasic3 = Kindle:new{
+local KindleBasic3 = Kindle:extend{
    model = "KindleBasic3",
    isRex = yes,
    -- NOTE: Apparently, the KT4 doesn't actually support the fancy nightmode waveforms, c.f., ko/#5076
@@ -582,7 +582,7 @@ local KindleBasic3 = Kindle:new{
    touch_dev = "/dev/input/event2",
 }

-local KindlePaperWhite5 = Kindle:new{
+local KindlePaperWhite5 = Kindle:extend{
    model = "KindlePaperWhite5",
    isMTK = yes,
    isTouchDevice = yes,
@@ -599,7 +599,7 @@ local KindlePaperWhite5 = Kindle:new{
    canDoSwipeAnimation = yes,
 }

-local KindleScribe = Kindle:new{
+local KindleScribe = Kindle:extend{
    model = "KindleScribe",
    isMTK = yes,
    isTouchDevice = yes,
--- a/frontend/device/kobo/device.lua
+++ b/frontend/device/kobo/device.lua
@@ -18,6 +18,7 @@ require("ffi/posix_h")

 local function yes() return true end
 local function no() return false end
+local function NOP() return end

 local function koboEnableWifi(toggle)
    if toggle == true then
@@ -131,7 +132,7 @@ local function getRTCName()
    end
 end

-local Kobo = Generic:new{
+local Kobo = Generic:extend{
    model = "Kobo",
    isKobo = yes,
    isTouchDevice = yes, -- all of them are
@@ -192,21 +193,21 @@ local Kobo = Generic:new{
 }

 -- Kobo Touch A/B:
-local KoboTrilogyAB = Kobo:new{
+local KoboTrilogyAB = Kobo:extend{
    model = "Kobo_trilogy_AB",
    touch_kobo_mk3_protocol = true,
    hasKeys = yes,
    hasMultitouch = no,
 }
 -- Kobo Touch C:
-local KoboTrilogyC = Kobo:new{
+local KoboTrilogyC = Kobo:extend{
    model = "Kobo_trilogy_C",
    hasKeys = yes,
    hasMultitouch = no,
 }

 -- Kobo Mini:
-local KoboPixie = Kobo:new{
+local KoboPixie = Kobo:extend{
    model = "Kobo_pixie",
    display_dpi = 200,
    hasMultitouch = no,
@@ -215,7 +216,7 @@ local KoboPixie = Kobo:new{
 }

 -- Kobo Aura One:
-local KoboDaylight = Kobo:new{
+local KoboDaylight = Kobo:extend{
    model = "Kobo_daylight",
    hasFrontlight = yes,
    touch_phoenix_protocol = true,
@@ -229,8 +230,10 @@ local KoboDaylight = Kobo:new{
 }

 -- Kobo Aura H2O:
-local KoboDahlia = Kobo:new{
+local KoboDahlia = Kobo:extend{
    model = "Kobo_dahlia",
+    canToggleChargingLED = no,  -- Possibly weird interactions with Nickel
+    led_uses_channel_3 = true,
    hasFrontlight = yes,
    touch_phoenix_protocol = true,
    -- There's no slot 0, the first finger gets assigned slot 1, and the second slot 2.
@@ -243,7 +246,7 @@ local KoboDahlia = Kobo:new{
 }

 -- Kobo Aura HD:
-local KoboDragon = Kobo:new{
+local KoboDragon = Kobo:extend{
    model = "Kobo_dragon",
    hasFrontlight = yes,
    hasMultitouch = no,
@@ -251,7 +254,7 @@ local KoboDragon = Kobo:new{
 }

 -- Kobo Glo:
-local KoboKraken = Kobo:new{
+local KoboKraken = Kobo:extend{
    model = "Kobo_kraken",
    hasFrontlight = yes,
    hasMultitouch = no,
@@ -259,7 +262,7 @@ local KoboKraken = Kobo:new{
 }

 -- Kobo Aura:
-local KoboPhoenix = Kobo:new{
+local KoboPhoenix = Kobo:extend{
    model = "Kobo_phoenix",
    hasFrontlight = yes,
    touch_phoenix_protocol = true,
@@ -273,7 +276,7 @@ local KoboPhoenix = Kobo:new{
 }

 -- Kobo Aura H2O2:
-local KoboSnow = Kobo:new{
+local KoboSnow = Kobo:extend{
    model = "Kobo_snow",
    hasFrontlight = yes,
    touch_snow_protocol = true,
@@ -289,7 +292,7 @@ local KoboSnow = Kobo:new{

 -- Kobo Aura H2O2, Rev2:
 --- @fixme Check if the Clara fix actually helps here... (#4015)
-local KoboSnowRev2 = Kobo:new{
+local KoboSnowRev2 = Kobo:extend{
    model = "Kobo_snow_r2",
    isMk7 = yes,
    hasFrontlight = yes,
@@ -303,7 +306,7 @@ local KoboSnowRev2 = Kobo:new{
 }

 -- Kobo Aura second edition:
-local KoboStar = Kobo:new{
+local KoboStar = Kobo:extend{
    model = "Kobo_star",
    hasFrontlight = yes,
    touch_phoenix_protocol = true,
@@ -311,7 +314,7 @@ local KoboStar = Kobo:new{
 }

 -- Kobo Aura second edition, Rev 2:
-local KoboStarRev2 = Kobo:new{
+local KoboStarRev2 = Kobo:extend{
    model = "Kobo_star_r2",
    isMk7 = yes,
    hasFrontlight = yes,
@@ -320,7 +323,7 @@ local KoboStarRev2 = Kobo:new{
 }

 -- Kobo Glo HD:
-local KoboAlyssum = Kobo:new{
+local KoboAlyssum = Kobo:extend{
    model = "Kobo_alyssum",
    hasFrontlight = yes,
    touch_phoenix_protocol = true,
@@ -329,14 +332,14 @@ local KoboAlyssum = Kobo:new{
 }

 -- Kobo Touch 2.0:
-local KoboPika = Kobo:new{
+local KoboPika = Kobo:extend{
    model = "Kobo_pika",
    touch_phoenix_protocol = true,
    main_finger_slot = 1,
 }

 -- Kobo Clara HD:
-local KoboNova = Kobo:new{
+local KoboNova = Kobo:extend{
    model = "Kobo_nova",
    isMk7 = yes,
    canToggleChargingLED = yes,
@@ -362,7 +365,7 @@ local KoboNova = Kobo:new{
 --       i.e., this will affect KSM users.
 --       c.f., https://github.com/koreader/koreader/pull/4414#issuecomment-449652335
 --       There's also a CM_ROTARY_ENABLE command, but which seems to do as much nothing as the STATUS one...
-local KoboFrost = Kobo:new{
+local KoboFrost = Kobo:extend{
    model = "Kobo_frost",
    isMk7 = yes,
    canToggleChargingLED = yes,
@@ -387,7 +390,7 @@ local KoboFrost = Kobo:new{

 -- Kobo Libra:
 -- NOTE: Assume the same quirks as the Forma apply.
-local KoboStorm = Kobo:new{
+local KoboStorm = Kobo:extend{
    model = "Kobo_storm",
    isMk7 = yes,
    canToggleChargingLED = yes,
@@ -418,7 +421,7 @@ local KoboStorm = Kobo:new{

 -- Kobo Nia:
 --- @fixme: Mostly untested, assume it's Clara-ish for now.
-local KoboLuna = Kobo:new{
+local KoboLuna = Kobo:extend{
    model = "Kobo_luna",
    isMk7 = yes,
    canToggleChargingLED = yes,
@@ -428,7 +431,7 @@ local KoboLuna = Kobo:new{
 }

 -- Kobo Elipsa
-local KoboEuropa = Kobo:new{
+local KoboEuropa = Kobo:extend{
    model = "Kobo_europa",
    isSunxi = yes,
    hasEclipseWfm = yes,
@@ -448,7 +451,7 @@ local KoboEuropa = Kobo:new{
 }

 -- Kobo Sage
-local KoboCadmus = Kobo:new{
+local KoboCadmus = Kobo:extend{
    model = "Kobo_cadmus",
    isSunxi = yes,
    hasEclipseWfm = yes,
@@ -481,7 +484,7 @@ local KoboCadmus = Kobo:new{
 }

 -- Kobo Libra 2:
-local KoboIo = Kobo:new{
+local KoboIo = Kobo:extend{
    model = "Kobo_io",
    isMk7 = yes,
    hasEclipseWfm = yes,
@@ -513,7 +516,7 @@ local KoboIo = Kobo:new{
 }

 -- Kobo Clara 2E:
-local KoboGoldfinch = Kobo:new{
+local KoboGoldfinch = Kobo:extend{
    model = "Kobo_goldfinch",
    isMk7 = yes,
    hasEclipseWfm = yes,
@@ -682,15 +685,15 @@ function Kobo:init()
    self.default_cpu_governor = getCPUGovernor(self.cpu_governor_knob)
    -- NOP unsupported methods
    if not self.default_cpu_governor then
-        self.performanceCPUGovernor = function() end
-        self.defaultCPUGovernor = function() end
+        self.performanceCPUGovernor = NOP
+        self.defaultCPUGovernor = NOP
    end

    -- And while we're on CPU-related endeavors...
    self.cpu_count = self:isSMP() and getCPUCount() or 1
    -- NOP unsupported methods
    if self.cpu_count == 1 then
-        self.enableCPUCores = function() end
+        self.enableCPUCores = NOP
    end

    -- Automagically set this so we never have to remember to do it manually ;p
@@ -742,6 +745,7 @@ function Kobo:init()
        dodgy_rtc = dodgy_rtc,
    }

+    -- Let generic properly setup the standard stuff
    Generic.init(self)

    -- Various HW Buttons, Switches & Synthetic NTX events
@@ -768,14 +772,14 @@ function Kobo:init()
    -- See if the device supports key repeat
    if not self:getKeyRepeat() then
        -- NOP unsupported methods
-        self.disableKeyRepeat = function() end
-        self.restoreKeyRepeat = function() end
+        self.disableKeyRepeat = NOP
+        self.restoreKeyRepeat = NOP
    end

    -- NOP unsupported methods
    if not self:canToggleChargingLED() then
-        self.toggleChargingLED = function() end
-        self.setupChargingLED = function() end
+        self.toggleChargingLED = NOP
+        self.setupChargingLED = NOP
    end

    -- We have no way of querying the current state of the charging LED, so, start from scratch.
@@ -1233,12 +1237,15 @@ function Kobo:toggleChargingLED(toggle)
    --       In fact, Nickel itself doesn't provide this feature on said older devices
    --       (when it does, it's an option in the Energy saving settings),
    --       which is why we also limit ourselves to "true" on devices where this was tested.
+    --       FWIW, on older devices, the knob is at "/sys/devices/platform/pmic_light.1/lit".
    -- c.f., drivers/misc/ntx_misc_light.c
    local f = io.open("/sys/devices/platform/ntx_led/lit", "we")
    if not f then
        logger.err("cannot open /sys/devices/platform/ntx_led/lit for writing!")
        return false
    end
+    -- Relying on LFs is mildly more elegant than spamming f:flush() calls ;).
+    C.setlinebuf(f)

    -- c.f., strace -fittTvyy -e trace=ioctl,file,signal,ipc,desc -s 256 -o /tmp/nickel.log -p $(pidof -s nickel) &
    -- This was observed on a Forma, so I'm mildly hopeful that it's safe on other Mk. 7 devices ;).
@@ -1247,38 +1254,13 @@ function Kobo:toggleChargingLED(toggle)
        -- NOTE: Technically, Nickel forces a toggle off before that, too.
        --       But since we do that on startup, it shouldn't be necessary here...
        if self.led_uses_channel_3 then
-            f:write("ch 3")
-            f:flush()
-            f:write("cur 1")
-            f:flush()
-            f:write("dc 63")
-            f:flush()
+            f:write("ch 3\n", "cur 1\n", "dc 63\n")
        end
-        f:write("ch 4")
-        f:flush()
-        f:write("cur 1")
-        f:flush()
-        f:write("dc 63")
-        f:flush()
+        f:write("ch 4\n", "cur 1\n", "dc 63\n")
    else
-        f:write("ch 3")
-        f:flush()
-        f:write("cur 1")
-        f:flush()
-        f:write("dc 0")
-        f:flush()
-        f:write("ch 4")
-        f:flush()
-        f:write("cur 1")
-        f:flush()
-        f:write("dc 0")
-        f:flush()
-        f:write("ch 5")
-        f:flush()
-        f:write("cur 1")
-        f:flush()
-        f:write("dc 0")
-        f:flush()
+        for ch = 3, 5 do
+            f:write("ch " .. tostring(ch) .. "\n", "cur 1\n", "dc 0\n")
+        end
    end

    f:close()
--- a/frontend/device/pocketbook/device.lua
+++ b/frontend/device/pocketbook/device.lua
@@ -21,7 +21,7 @@ local function no() return false end
 local ext_path = "/mnt/ext1/system/config/extensions.cfg"
 local app_name = "koreader.app"

-local PocketBook = Generic:new{
+local PocketBook = Generic:extend{
    model = "PocketBook",
    isPocketBook = yes,
    hasOTAUpdates = yes,
@@ -407,7 +407,7 @@ local function landscape_ccw() return {
 } end

 -- PocketBook Mini (515)
-local PocketBook515 = PocketBook:new{
+local PocketBook515 = PocketBook:extend{
    model = "PB515",
    display_dpi = 200,
    isTouchDevice = no,
@@ -417,7 +417,7 @@ local PocketBook515 = PocketBook:new{
 }

 -- PocketBook Basic 4 (606)
-local PocketBook606 = PocketBook:new{
+local PocketBook606 = PocketBook:extend{
    model = "PB606",
    display_dpi = 212,
    isTouchDevice = no,
@@ -427,7 +427,7 @@ local PocketBook606 = PocketBook:new{
 }

 -- PocketBook Basic (611)
-local PocketBook611 = PocketBook:new{
+local PocketBook611 = PocketBook:extend{
    model = "PB611",
    display_dpi = 167,
    isTouchDevice = no,
@@ -437,7 +437,7 @@ local PocketBook611 = PocketBook:new{
 }

 -- PocketBook Basic (613)
-local PocketBook613 = PocketBook:new{
+local PocketBook613 = PocketBook:extend{
    model = "PB613B",
    display_dpi = 167,
    isTouchDevice = no,
@@ -448,7 +448,7 @@ local PocketBook613 = PocketBook:new{
 }

 -- PocketBook Basic 2 / Basic 3 (614/614W)
-local PocketBook614W = PocketBook:new{
+local PocketBook614W = PocketBook:extend{
    model = "PB614W",
    display_dpi = 167,
    isTouchDevice = no,
@@ -458,7 +458,7 @@ local PocketBook614W = PocketBook:new{
 }

 -- PocketBook Basic Lux / 615 Plus (615/615W)
-local PocketBook615 = PocketBook:new{
+local PocketBook615 = PocketBook:extend{
    model = "PBBLux",
    display_dpi = 212,
    isTouchDevice = no,
@@ -467,7 +467,7 @@ local PocketBook615 = PocketBook:new{
 }

 -- PocketBook Basic Lux 2 (616/616W)
-local PocketBook616 = PocketBook:new{
+local PocketBook616 = PocketBook:extend{
    model = "PBBLux2",
    display_dpi = 212,
    isTouchDevice = no,
@@ -476,7 +476,7 @@ local PocketBook616 = PocketBook:new{
 }

 -- PocketBook Basic Lux 3 (617)
-local PocketBook617 = PocketBook:new{
+local PocketBook617 = PocketBook:extend{
    model = "PBBLux3",
    display_dpi = 212,
    isTouchDevice = no,
@@ -486,47 +486,47 @@ local PocketBook617 = PocketBook:new{
 }

 -- PocketBook Touch (622)
-local PocketBook622 = PocketBook:new{
+local PocketBook622 = PocketBook:extend{
    model = "PBTouch",
    display_dpi = 167,
    hasFrontlight = no,
 }

 -- PocketBook Touch Lux (623)
-local PocketBook623 = PocketBook:new{
+local PocketBook623 = PocketBook:extend{
    model = "PBTouchLux",
    display_dpi = 212,
 }

 -- PocketBook Basic Touch (624)
-local PocketBook624 = PocketBook:new{
+local PocketBook624 = PocketBook:extend{
    model = "PBBasicTouch",
    display_dpi = 167,
    hasFrontlight = no,
 }

 -- PocketBook Basic Touch 2 (625)
-local PocketBook625 = PocketBook:new{
+local PocketBook625 = PocketBook:extend{
    model = "PBBasicTouch2",
    display_dpi = 167,
    hasFrontlight = no,
 }

 -- PocketBook Touch Lux 2 / Touch Lux 3 (626)
-local PocketBook626 = PocketBook:new{
+local PocketBook626 = PocketBook:extend{
    model = "PBLux3",
    display_dpi = 212,
 }

 -- PocketBook Touch Lux 4 (627)
-local PocketBook627 = PocketBook:new{
+local PocketBook627 = PocketBook:extend{
    model = "PBLux4",
    display_dpi = 212,
    isAlwaysPortrait = yes,
 }

 -- PocketBook Touch Lux 5 (628)
-local PocketBook628 = PocketBook:new{
+local PocketBook628 = PocketBook:extend{
    model = "PBTouchLux5",
    display_dpi = 212,
    isAlwaysPortrait = yes,
@@ -535,13 +535,13 @@ local PocketBook628 = PocketBook:new{
 }

 -- PocketBook Sense / Sense 2 (630)
-local PocketBook630 = PocketBook:new{
+local PocketBook630 = PocketBook:extend{
    model = "PBSense",
    display_dpi = 212,
 }

 -- PocketBook Touch HD / Touch HD 2 (631)
-local PocketBook631 = PocketBook:new{
+local PocketBook631 = PocketBook:extend{
    model = "PBTouchHD",
    display_dpi = 300,
    -- see https://github.com/koreader/koreader/pull/6531#issuecomment-676629182
@@ -549,7 +549,7 @@ local PocketBook631 = PocketBook:new{
 }

 -- PocketBook Touch HD Plus / Touch HD 3 (632)
-local PocketBook632 = PocketBook:new{
+local PocketBook632 = PocketBook:extend{
    model = "PBTouchHDPlus",
    display_dpi = 300,
    isAlwaysPortrait = yes,
@@ -558,7 +558,7 @@ local PocketBook632 = PocketBook:new{
 }

 -- PocketBook Color (633)
-local PocketBook633 = PocketBook:new{
+local PocketBook633 = PocketBook:extend{
    model = "PBColor",
    display_dpi = 300,
    hasColorScreen = yes,
@@ -568,25 +568,25 @@ local PocketBook633 = PocketBook:new{
 }

 -- PocketBook Aqua (640)
-local PocketBook640 = PocketBook:new{
+local PocketBook640 = PocketBook:extend{
    model = "PBAqua",
    display_dpi = 167,
 }

 -- PocketBook Aqua 2 (641)
-local PocketBook641 = PocketBook:new{
+local PocketBook641 = PocketBook:extend{
    model = "PBAqua2",
    display_dpi = 212,
 }

 -- PocketBook Ultra (650)
-local PocketBook650 = PocketBook:new{
+local PocketBook650 = PocketBook:extend{
    model = "PBUltra",
    display_dpi = 212,
 }

 -- PocketBook Era (700)
-local PocketBook700 = PocketBook:new{
+local PocketBook700 = PocketBook:extend{
    model = "PB700",
    display_dpi = 300,
    isAlwaysPortrait = yes,
@@ -594,7 +594,7 @@ local PocketBook700 = PocketBook:new{
 }

 -- PocketBook InkPad 3 (740)
-local PocketBook740 = PocketBook:new{
+local PocketBook740 = PocketBook:extend{
    model = "PBInkPad3",
    display_dpi = 300,
    isAlwaysPortrait = yes,
@@ -603,7 +603,7 @@ local PocketBook740 = PocketBook:new{
 }

 -- PocketBook InkPad 3 Pro (740_2)
-local PocketBook740_2 = PocketBook:new{
+local PocketBook740_2 = PocketBook:extend{
    model = "PBInkPad3Pro",
    display_dpi = 300,
    isAlwaysPortrait = yes,
@@ -620,7 +620,7 @@ local PocketBook740_2 = PocketBook:new{
 }

 -- PocketBook InkPad Color (741)
-local PocketBook741 = PocketBook:new{
+local PocketBook741 = PocketBook:extend{
    model = "PBInkPadColor",
    display_dpi = 300,
    hasColorScreen = yes,
@@ -635,7 +635,7 @@ function PocketBook741._fb_init(fb, finfo, vinfo)
 end

 -- PocketBook Color Lux (801)
-local PocketBookColorLux = PocketBook:new{
+local PocketBookColorLux = PocketBook:extend{
    model = "PBColorLux",
    display_dpi = 125,
    hasColorScreen = yes,
@@ -653,13 +653,13 @@ function PocketBookColorLux._fb_init(fb, finfo, vinfo)
 end

 -- PocketBook InkPad / InkPad 2 (840)
-local PocketBook840 = PocketBook:new{
+local PocketBook840 = PocketBook:extend{
    model = "PBInkPad",
    display_dpi = 250,
 }

 -- PocketBook InkPad Lite (970)
-local PocketBook970 = PocketBook:new{
+local PocketBook970 = PocketBook:extend{
    model = "PB970",
    display_dpi = 150,
    isAlwaysPortrait = yes,
@@ -667,7 +667,7 @@ local PocketBook970 = PocketBook:new{
 }

 -- PocketBook InkPad X (1040)
-local PocketBook1040 = PocketBook:new{
+local PocketBook1040 = PocketBook:extend{
    model = "PB1040",
    display_dpi = 227,
    isAlwaysPortrait = yes,
--- a/frontend/device/remarkable/device.lua
+++ b/frontend/device/remarkable/device.lua
@@ -29,7 +29,7 @@ local wacom_scale_x = screen_width / wacom_width
 local wacom_scale_y = screen_height / wacom_height
 local isRm2, rm_model = getModel()

-local Remarkable = Generic:new{
+local Remarkable = Generic:extend{
    isRemarkable = yes,
    model = rm_model,
    hasKeys = yes,
@@ -47,7 +47,7 @@ local Remarkable = Generic:new{
    home_dir = "/home/root",
 }

-local Remarkable1 = Remarkable:new{
+local Remarkable1 = Remarkable:extend{
    mt_width = 767, -- unscaled_size_check: ignore
    mt_height = 1023, -- unscaled_size_check: ignore
    input_wacom = "/dev/input/event0",
@@ -70,7 +70,7 @@ function Remarkable1:adjustTouchEvent(ev, by)
    end
 end

-local Remarkable2 = Remarkable:new{
+local Remarkable2 = Remarkable:extend{
    mt_width = 1403, -- unscaled_size_check: ignore
    mt_height = 1871, -- unscaled_size_check: ignore
    input_wacom = "/dev/input/event1",
--- a/frontend/device/sdl/device.lua
+++ b/frontend/device/sdl/device.lua
@@ -60,7 +60,7 @@ local external = require("device/thirdparty"):new{
    end,
 }

-local Device = Generic:new{
+local Device = Generic:extend{
    model = "SDL",
    isSDL = yes,
    home_dir = os.getenv("XDG_DOCUMENTS_DIR") or os.getenv("HOME"),
@@ -105,21 +105,21 @@ local Device = Generic:new{
    window = G_reader_settings:readSetting("sdl_window", {}),
 }

-local AppImage = Device:new{
+local AppImage = Device:extend{
    model = "AppImage",
    hasMultitouch = no,
    hasOTAUpdates = yes,
    isDesktop = yes,
 }

-local Desktop = Device:new{
+local Desktop = Device:extend{
    model = SDL.getPlatform(),
    isDesktop = yes,
    canRestart = notOSX,
    hasExitOptions = notOSX,
 }

-local Emulator = Device:new{
+local Emulator = Device:extend{
    model = "Emulator",
    isEmulator = yes,
    hasBattery = yes,
@@ -137,7 +137,7 @@ local Emulator = Device:new{
    canStandby = no,
 }

-local UbuntuTouch = Device:new{
+local UbuntuTouch = Device:extend{
    model = "UbuntuTouch",
    hasFrontlight = yes,
    isDefaultFullscreen = yes,
--- a/frontend/device/sony-prstux/device.lua
+++ b/frontend/device/sony-prstux/device.lua
@@ -9,7 +9,7 @@ require("ffi/linux_input_h")
 local function yes() return true end
 local function no() return false end

-local SonyPRSTUX = Generic:new{
+local SonyPRSTUX = Generic:extend{
    model = "Sony PRSTUX",
    isSonyPRSTUX = yes,
    hasKeys = yes,
@@ -239,7 +239,7 @@ function SonyPRSTUX:setEventHandlers(UIManager)
 end

 -- For Sony PRS-T2
-local SonyPRSTUX_T2 = SonyPRSTUX:new{
+local SonyPRSTUX_T2 = SonyPRSTUX:extend{
    isTouchDevice = yes,
    hasKeys = yes,
    hasFrontlight = no,
--- a/frontend/device/wakeupmgr.lua
+++ b/frontend/device/wakeupmgr.lua
@@ -21,7 +21,7 @@ WakeupMgr base class.
 --]]
 local WakeupMgr = {
    dev_rtc = "/dev/rtc0", -- RTC device
-    _task_queue = {},      -- Table with epoch at which to schedule the task and the function to be scheduled.
+    _task_queue = nil,      -- Table with epoch at which to schedule the task and the function to be scheduled.
    rtc = RTC, -- The RTC implementation to use, defaults to the RTC module.
    dodgy_rtc = false, -- If the RTC has trouble with timers further away than UINT16_MAX (e.g., on i.MX5).
 }
@@ -45,6 +45,10 @@ function WakeupMgr:new(o)
    return o
 end

+function WakeupMgr:init()
+    self._task_queue = {}
+end
+
 -- This is a dummy task we use when working around i.MX5 RTC issues.
 -- We need to be able to recognize it so that we can deal with it in removeTasks...
 function WakeupMgr.DummyTaskCallback()
--- a/frontend/docsettings.lua
+++ b/frontend/docsettings.lua
@@ -5,13 +5,14 @@ in the so-called sidecar directory
 ]]

 local DataStorage = require("datastorage")
+local LuaSettings = require("luasettings")
 local dump = require("dump")
 local ffiutil = require("ffi/util")
 local lfs = require("libs/libkoreader-lfs")
 local logger = require("logger")
 local util = require("util")

-local DocSettings = {}
+local DocSettings = LuaSettings:extend{}

 local HISTORY_DIR = DataStorage:getHistoryDir()

@@ -102,18 +103,20 @@ end
 -- @treturn DocSettings object
 function DocSettings:open(docfile)
    --- @todo (zijiehe): Remove history_path, use only sidecar.
-    local new = {}
-    new.history_file = self:getHistoryPath(docfile)

-    local sidecar = self:getSidecarDir(docfile)
+    -- NOTE: Beware, our new instance is new, but self is still DocSettings!
+    local new = DocSettings:extend{}
+    new.history_file = new:getHistoryPath(docfile)
+
+    local sidecar = new:getSidecarDir(docfile)
    new.sidecar = sidecar
    DocSettings:ensureSidecar(sidecar)
-    -- If there is a file which has a same name as the sidecar directory, or
-    -- the file system is read-only, we should not waste time to read it.
+    -- If there is a file which has a same name as the sidecar directory,
+    -- or the file system is read-only, we should not waste time to read it.
    if lfs.attributes(sidecar, "mode") == "directory" then
-        -- New sidecar file name is metadata.{file last suffix}.lua. So we
-        -- can handle two files with only different suffixes.
-        new.sidecar_file = self:getSidecarFile(docfile)
+        -- New sidecar file name is metadata.{file last suffix}.lua.
+        -- So we can handle two files with only different suffixes.
+        new.sidecar_file = new:getSidecarFile(docfile)
        new.legacy_sidecar_file = sidecar.."/"..
                                  ffiutil.basename(docfile)..".lua"
    end
@@ -163,139 +166,7 @@ function DocSettings:open(docfile)
        new.data = {}
    end

-    return setmetatable(new, {__index = DocSettings})
-end
-
--[[-- Reads a setting, optionally initializing it to a default.
-
-If default is provided, and the key doesn't exist yet, it is initialized to default first.
-This ensures both that the defaults are actually set if necessary,
-and that the returned reference actually belongs to the DocSettings object straight away,
-without requiring further interaction (e.g., saveSetting) from the caller.
-
-This is mainly useful if the data type you want to retrieve/store is assigned/returned/passed by reference (e.g., a table),
-and you never actually break that reference by assigning another one to the same variable, (by e.g., assigning it a new object).
-c.f., https://www.lua.org/manual/5.1/manual.html#2.2
-
-@param key The setting's key
-@param default Initialization data (Optional)
-]]
-function DocSettings:readSetting(key, default)
-    -- No initialization data: legacy behavior
-    if not default then
-        return self.data[key]
-    end
-
-    if not self:has(key) then
-        self.data[key] = default
-    end
-    return self.data[key]
-end
-
--- Saves a setting.
-function DocSettings:saveSetting(key, value)
-    self.data[key] = value
-    return self
-end
-
--- Deletes a setting.
-function DocSettings:delSetting(key)
-    self.data[key] = nil
-    return self
-end
-
--- Checks if setting exists.
-function DocSettings:has(key)
-    return self.data[key] ~= nil
-end
-
--- Checks if setting does not exist.
-function DocSettings:hasNot(key)
-    return self.data[key] == nil
-end
-
--- Checks if setting is `true` (boolean).
-function DocSettings:isTrue(key)
-    return self.data[key] == true
-end
-
--- Checks if setting is `false` (boolean).
-function DocSettings:isFalse(key)
-    return self.data[key] == false
-end
-
--- Checks if setting is `nil` or `true`.
-function DocSettings:nilOrTrue(key)
-    return self:hasNot(key) or self:isTrue(key)
-end
-
--- Checks if setting is `nil` or `false`.
-function DocSettings:nilOrFalse(key)
-    return self:hasNot(key) or self:isFalse(key)
-end
-
--- Flips `nil` or `true` to `false`, and `false` to `nil`.
--- e.g., a setting that defaults to true.
-function DocSettings:flipNilOrTrue(key)
-    if self:nilOrTrue(key) then
-        self:saveSetting(key, false)
-    else
-        self:delSetting(key)
-    end
-    return self
-end
-
--- Flips `nil` or `false` to `true`, and `true` to `nil`.
--- e.g., a setting that defaults to false.
-function DocSettings:flipNilOrFalse(key)
-    if self:nilOrFalse(key) then
-        self:saveSetting(key, true)
-    else
-        self:delSetting(key)
-    end
-    return self
-end
-
--- Flips a setting between `true` and `nil`.
-function DocSettings:flipTrue(key)
-    if self:isTrue(key) then
-        self:delSetting(key)
-    else
-        self:saveSetting(key, true)
-    end
-    return self
-end
-
--- Flips a setting between `false` and `nil`.
-function DocSettings:flipFalse(key)
-    if self:isFalse(key) then
-        self:delSetting(key)
-    else
-        self:saveSetting(key, false)
-    end
-    return self
-end
-
-- Unconditionally makes a boolean setting `true`.
-function DocSettings:makeTrue(key)
-    self:saveSetting(key, true)
-    return self
-end
-
-- Unconditionally makes a boolean setting `false`.
-function DocSettings:makeFalse(key)
-    self:saveSetting(key, false)
-    return self
-end
-
--- Toggles a boolean setting
-function DocSettings:toggle(key)
-    if self:nilOrFalse(key) then
-        self:saveSetting(key, true)
-    else
-        self:saveSetting(key, false)
-    end
-    return self
+    return new
 end

 --- Serializes settings and writes them to `metadata.lua`.
@@ -307,8 +178,7 @@ function DocSettings:flush()
        return
    end

-    -- If we can write to sidecar_file, we do not need to write to history_file
-    -- anymore.
+    -- If we can write to sidecar_file, we do not need to write to history_file anymore.
    local serials = {}
    if self.sidecar_file then
        table.insert(serials, self.sidecar_file)
@@ -322,11 +192,10 @@ function DocSettings:flush()
    for _, f in ipairs(serials) do
        local directory_updated = false
        if lfs.attributes(f, "mode") == "file" then
-            -- As an additional safety measure (to the ffiutil.fsync* calls
-            -- used below), we only backup the file to .old when it has
-            -- not been modified in the last 60 seconds. This should ensure
-            -- in the case the fsync calls are not supported that the OS
-            -- may have itself sync'ed that file content in the meantime.
+            -- As an additional safety measure (to the ffiutil.fsync* calls used below),
+            -- we only backup the file to .old when it has not been modified in the last 60 seconds.
+            -- This should ensure in the case the fsync calls are not supported
+            -- that the OS may have itself sync'ed that file content in the meantime.
            local mtime = lfs.attributes(f, "modification")
            if mtime < os.time() - 60 then
                logger.dbg("Rename ", f, " to ", f .. ".old")
@@ -364,18 +233,13 @@ function DocSettings:flush()
    end
 end

-function DocSettings:close()
-    self:flush()
-end
-
 function DocSettings:getFilePath()
    return self.filepath
 end

 --- Purges (removes) sidecar directory.
 function DocSettings:purge(full)
-    -- Remove any of the old ones we may consider as candidates
-    -- in DocSettings:open()
+    -- Remove any of the old ones we may consider as candidates in DocSettings:open()
    if self.history_file then
        os.remove(self.history_file)
        os.remove(self.history_file .. ".old")
@@ -385,12 +249,10 @@ function DocSettings:purge(full)
    end
    if lfs.attributes(self.sidecar, "mode") == "directory" then
        if full then
-            -- Asked to remove all the content of this .sdr directory,
-            -- whether it's ours or not
+            -- Asked to remove all the content of this .sdr directory, whether it's ours or not
            ffiutil.purgeDir(self.sidecar)
        else
-            -- Only remove the files we know we may have created
-            -- with our usual names.
+            -- Only remove the files we know we may have created with our usual names.
            for f in lfs.dir(self.sidecar) do
                local fullpath = self.sidecar.."/"..f
                local to_remove = false
@@ -398,8 +260,8 @@ function DocSettings:purge(full)
                    -- Currently, we only create a single file in there,
                    -- named metadata.suffix.lua (ie. metadata.epub.lua),
                    -- with possibly backups named metadata.epub.lua.old and
-                    -- metadata.epub.lua.old_dom20180528, so all sharing the
-                    -- same base: self.sidecar_file
+                    -- metadata.epub.lua.old_dom20180528,
+                    -- so all sharing the same base: self.sidecar_file
                    if util.stringStartsWith(fullpath, self.sidecar_file) then
                        to_remove = true
                    end
@@ -414,8 +276,8 @@ function DocSettings:purge(full)
            os.remove(self.sidecar)
        end
    end
-    -- We should have meet the candidate we used and remove it above. But in
-    -- case we didn't, remove it
+    -- We should have meet the candidate we used and remove it above.
+    -- But in case we didn't, remove it.
    if self.filepath and lfs.attributes(self.filepath, "mode") == "file" then
        os.remove(self.filepath)
    end
--- a/frontend/document/canvascontext.lua
+++ b/frontend/document/canvascontext.lua
@@ -14,7 +14,6 @@ Note: CanvasContext is a singleton and it is not thread safe.
 local Mupdf = require("ffi/mupdf")

 local CanvasContext = {
-    should_restrict_JIT = false,
    is_color_rendering_enabled = false,
    is_bgr = false,
 }
@@ -24,7 +23,6 @@ Initialize CanvasContext with settings from device.

 The following key is required for a device object:

-* should_restrict_JIT: bool
 * hasBGRFrameBuffer: function() -> boolean
 * screen: object with following methods:
    * getWidth() -> int
@@ -51,7 +49,6 @@ function CanvasContext:init(device)
    self.isEmulator = device.isEmulator
    self.isKindle = device.isKindle
    self.isPocketBook = device.isPocketBook
-    self.should_restrict_JIT = device.should_restrict_JIT
    self.hasSystemFonts = device.hasSystemFonts
    self:setColorRenderingEnabled(device.screen:isColorEnabled())

--- a/frontend/document/credocument.lua
+++ b/frontend/document/credocument.lua
@@ -18,7 +18,7 @@ local time = require("ui/time")
 -- engine can be initialized only once, on first document opened
 local engine_initialized = false

-local CreDocument = Document:new{
+local CreDocument = Document:extend{
    -- this is defined in kpvcrlib/crengine/crengine/include/lvdocview.h
    SCROLL_VIEW_MODE = 0,
    PAGE_VIEW_MODE = 1,
@@ -49,7 +49,7 @@ local CreDocument = Document:new{
    --   require one to set FreeSans as fallback to get its nicer glyphes, which
    --   would override Noto Sans CJK good symbol glyphs with smaller ones
    --   (Noto Sans & Serif do not have these symbol glyphs).
-    fallback_fonts = {
+    fallback_fonts = { -- const
        "Noto Sans CJK SC",
        "Noto Naskh Arabic",
        "Noto Sans Devanagari UI",
@@ -65,8 +65,8 @@ local CreDocument = Document:new{
    provider_name = "Cool Reader Engine",

    hide_nonlinear_flows = false,
-    flows = {},
-    page_in_flow = {},
+    flows = nil, -- table
+    page_in_flow = nil, -- table
    last_linear_page = nil,
 }

@@ -147,6 +147,9 @@ function CreDocument:init()
    self:updateColorRendering()
    self:engineInit()

+    self.flows = {}
+    self.page_in_flow = {}
+
    local file_type = string.lower(string.match(self.file, ".+%.([^.]+)"))
    if file_type == "zip" then
        -- NuPogodi, 20.05.12: read the content of zip-file
@@ -331,9 +334,11 @@ function CreDocument:close()
        end

        -- Only exists if the call cache is enabled
+        --[[
        if self._callCacheDestroy then
            self._callCacheDestroy()
        end
+        --]]
    end
 end

@@ -1510,14 +1515,27 @@ function CreDocument:setupCallCache()
        -- Stores the key for said current tag
        self._current_call_cache_tag = nil
    end
+    --[[
+    --- @note: If explicitly destroying the references to the caches is necessary to get their content collected by the GC,
+    ---        then you have a ref leak to this Document instance somewhere,
+    ---        c.f., https://github.com/koreader/koreader/pull/7634#discussion_r627820424
+    ---        Keep in mind that a *lot* of ReaderUI modules keep a ref to document, so it may be fairly remote!
+    ---        A good contender for issues like these would be references being stored in the class object instead
+    ---        of in instance objects because of inheritance rules. c.f., https://github.com/koreader/koreader/pull/9586,
+    ---        which got rid of a giant leak of every ReaderUI module via the active_widgets array...
+    ---        A simple testing methodology is to create a dummy buffer alongside self.buffer in drawCurrentView,
+    ---        push it to the global cache via _callCacheSet, and trace the BlitBuffer gc method in ffi/blitbuffer.lua.
+    ---        You'll probably want to stick a pair of collectgarbage() calls somewhere in the UI loop
+    ---        (e.g., at the coda of UIManager:close) to trip a GC pass earlier than the one in DocumentRegistry:openDocument.
+    ---        (Keep in mind that, in UIManager:close, widget is still in scope inside the function,
+    ---        so you'll have to close another widget to truly collect it (here, ReaderUI)).
    self._callCacheDestroy = function()
-        --- @note: Explicitly destroying the references to the caches is apparently necessary to get their content collected by the GC...
-        ---        c.f., https://github.com/koreader/koreader/pull/7634#discussion_r627820424
        self._global_call_cache = nil
        self._tag_list_call_cache = nil
        self._tag_call_cache = nil
        self._current_call_cache_tag = nil
    end
+    --]]
    -- global cache
    self._callCacheGet = function(key)
        return self._global_call_cache[key]
--- a/frontend/document/djvudocument.lua
+++ b/frontend/document/djvudocument.lua
@@ -2,7 +2,7 @@ local Blitbuffer = require("ffi/blitbuffer")
 local Document = require("document/document")
 local DrawContext = require("ffi/drawcontext")

-local DjvuDocument = Document:new{
+local DjvuDocument = Document:extend{
    _document = false,
    -- libdjvulibre manages its own additional cache, default value is hard written in c module.
    is_djvu = true,
--- a/frontend/document/doccache.lua
+++ b/frontend/document/doccache.lua
@@ -45,6 +45,7 @@ local function computeCacheSlots()
    end
 end

+-- NOTE: This is a singleton!
 local DocCache = Cache:new{
    slots = computeCacheSlots(),
    size = computeCacheSize(),
--- a/frontend/document/document.lua
+++ b/frontend/document/document.lua
@@ -16,13 +16,15 @@ This is an abstract interface to a document
 local Document = {
    -- file name
    file = nil,
+    -- engine instance
+    _document = nil,

-    links = {},
+    links = nil, -- table

    GAMMA_NO_GAMMA = 1.0,

    -- override bbox from orignal page's getUsedBBox
-    bbox = {},
+    bbox = nil, -- table

    -- flag to show whether the document was opened successfully
    is_open = false,
@@ -40,10 +42,15 @@ local Document = {

 }

-function Document:new(from_o)
-    local o = from_o or {}
+function Document:extend(subclass_prototype)
+    local o = subclass_prototype or {}
    setmetatable(o, self)
    self.__index = self
+    return o
+end
+
+function Document:new(o)
+    o = self:extend(o)
    if o._init then o:_init() end
    if o.init then o:init() end
    return o
@@ -51,7 +58,9 @@ end

 -- base document initialization should be called on each document init
 function Document:_init()
-    self.configurable = Configurable:new()
+    self.links = {}
+    self.bbox = {}
+    self.configurable = Configurable:new{}
    self.info = {
        -- whether the document is pageable
        has_pages = false,
--- a/frontend/document/documentregistry.lua
+++ b/frontend/document/documentregistry.lua
@@ -23,8 +23,8 @@ function DocumentRegistry:addProvider(extension, mimetype, provider, weight)
    })
    self.filetype_provider[extension] = true
    -- We regard the first extension registered for a mimetype as canonical.
-    -- Provided we order the calls to addProvider() correctly, that means
-    -- epub instead of epub3, etc.
+    -- Provided we order the calls to addProvider() correctly,
+    -- that means epub instead of epub3, etc.
    self.mimetype_ext[mimetype] = self.mimetype_ext[mimetype] or extension
 end

--- a/frontend/document/pdfdocument.lua
+++ b/frontend/document/pdfdocument.lua
@@ -10,7 +10,7 @@ local ffi = require("ffi")
 local C = ffi.C
 local pdf = nil

-local PdfDocument = Document:new{
+local PdfDocument = Document:extend{
    _document = false,
    is_pdf = true,
    dc_null = DrawContext.new(),
--- a/frontend/document/picdocument.lua
+++ b/frontend/document/picdocument.lua
@@ -3,7 +3,7 @@ local DrawContext = require("ffi/drawcontext")
 local CanvasContext = require("document/canvascontext")
 local pic = nil

-local PicDocument = Document:new{
+local PicDocument = Document:extend{
    _document = false,
    is_pic = true,
    dc_null = DrawContext.new(),
--- a/frontend/document/tilecacheitem.lua
+++ b/frontend/document/tilecacheitem.lua
@@ -3,7 +3,7 @@ local CacheItem = require("cacheitem")
 local Persist = require("persist")
 local logger = require("logger")

-local TileCacheItem = CacheItem:new{}
+local TileCacheItem = CacheItem:extend{}

 function TileCacheItem:onFree()
    logger.dbg("TileCacheItem: free blitbuffer", self.bb)
--- a/frontend/dump.lua
+++ b/frontend/dump.lua
@@ -1,5 +1,7 @@
 --[[--
 A simple serialization function which won't do uservalues, functions, or loops.
+
+If we ever need a more full-featured variant, the consensus seems to be https://github.com/pkulchenko/serpent ;).
 ]]

 local isUbuntuTouch = os.getenv("UBUNTU_APPLICATION_ISOLATION") ~= nil
@@ -15,7 +17,8 @@ local function _serialize(what, outt, indent, max_lv, history, pairs_func)
        return
    end

-    if type(what) == "table" then
+    local datatype = type(what)
+    if datatype == "table" then
        history = history or {}
        for up, item in ipairs(history) do
            if item == what then
@@ -43,9 +46,9 @@ local function _serialize(what, outt, indent, max_lv, history, pairs_func)
            insert(outt, string.rep(indent_prefix, indent))
        end
        insert(outt, "}")
-    elseif type(what) == "string" then
+    elseif datatype == "string" then
        insert(outt, string.format("%q", what))
-    elseif type(what) == "number" then
+    elseif datatype == "number" then
        if isUbuntuTouch then
            --- @fixme The `SDL_CreateRenderer` function in Ubuntu touch somehow
            -- use a strange locale that formats number like this: 1.10000000000000g+02
@@ -55,11 +58,11 @@ local function _serialize(what, outt, indent, max_lv, history, pairs_func)
        else
            insert(outt, tostring(what))
        end
-    elseif type(what) == "boolean" then
+    elseif datatype == "boolean" then
        insert(outt, tostring(what))
-    elseif type(what) == "function" then
+    elseif datatype == "function" then
        insert(outt, tostring(what))
-    elseif type(what) == "nil" then
+    elseif datatype == "nil" then
        insert(outt, "nil")
    end
 end
--- a/frontend/languagesupport.lua
+++ b/frontend/languagesupport.lua
@@ -2,7 +2,7 @@
 Language-specific handling module.

 This module defines a somewhat generic system by which language-specific
-plugins can improve KoReader's support for languages that are not close enough
+plugins can improve KOReader's support for languages that are not close enough
 to European languages to "just work".

 This was originally designed to improve KoReader's Japanese support through the
@@ -29,10 +29,10 @@ local _ = require("gettext")
 -- plugins when reloading different viewers.
 local PluginListSingleton = {}

-local LanguageSupport = WidgetContainer:new({
+local LanguageSupport = WidgetContainer:extend{
    name = "language_support",
    plugins = PluginListSingleton,
-})
+}

 --[[--
 Registers a new language-specific plugin with given language_code.
--- a/frontend/luadata.lua
+++ b/frontend/luadata.lua
@@ -3,31 +3,29 @@ Handles append-mostly data such as KOReader's bookmarks and dictionary search hi
 ]]

 local LuaSettings = require("luasettings")
-local dbg = require("dbg")
 local dump = require("dump")
 local lfs = require("libs/libkoreader-lfs")
 local logger = require("logger")
 local util = require("util")

-local LuaData = LuaSettings:new{
+local LuaData = LuaSettings:extend{
    name = "",
    max_backups = 9,
 }

 --- Creates a new LuaData instance.
-function LuaData:open(file_path, o) -- luacheck: ignore 312
-    if o and type(o) ~= "table" then
-        if dbg.is_on then
-            error("LuaData: got "..type(o)..", table expected")
-        else
-            o = {}
-        end
+function LuaData:open(file_path, name)
+    -- Backwards compat, just in case...
+    if type(name) == "table" then
+        name = name.name
    end
-    -- always initiate a new instance
-    -- careful, `o` is already a table so we use parentheses
-    self = LuaData:new(o)

-    local new = {file=file_path, data={}}
+    -- NOTE: Beware, our new instance is new, but self is still LuaData!
+    local new = LuaData:extend{
+        name = name,
+        file = file_path,
+        data = {},
+    }

    -- Some magic to allow for self-describing function names:
    -- We'll use data_env both as the environment when loading the data, *and* its metatable,
@@ -40,7 +38,7 @@ function LuaData:open(file_path, o) -- luacheck: ignore 312
    local data_env = {}
    data_env.__index = data_env
    setmetatable(data_env, data_env)
-    data_env[self.name.."Entry"] = function(table)
+    data_env[new.name.."Entry"] = function(table)
        if table.index then
            -- We've got a deleted setting, overwrite with nil and be done with it.
            if not table.data then
@@ -81,7 +79,7 @@ function LuaData:open(file_path, o) -- luacheck: ignore 312
        end
    end
    if not ok then
-        for i=1, self.max_backups, 1 do
+        for i=1, new.max_backups, 1 do
            local backup_file = new.file..".old."..i
            if lfs.attributes(backup_file, "mode") == "file" then
                ok, err = loadfile(backup_file, "t", data_env)
@@ -97,7 +95,7 @@ function LuaData:open(file_path, o) -- luacheck: ignore 312
        end
    end

-    return setmetatable(new, {__index = self})
+    return new
 end

 --- Saves a setting.
--- a/frontend/luadefaults.lua
+++ b/frontend/luadefaults.lua
@@ -11,7 +11,7 @@ local isAndroid, android = pcall(require, "android")
 local lfs = require("libs/libkoreader-lfs")
 local logger = require("logger")

-local LuaDefaults = LuaSettings:new{
+local LuaDefaults = LuaSettings:extend{
    ro = nil, -- will contain the defaults.lua k/v pairs (const)
    rw = nil, -- will only contain non-defaults user-modified k/v pairs
 }
@@ -19,7 +19,9 @@ local LuaDefaults = LuaSettings:new{
 --- Opens a settings file.
 function LuaDefaults:open(path)
    local file_path = path or DataStorage:getDataDir() .. "/defaults.custom.lua"
-    local new = {file = file_path}
+    local new = LuaDefaults:extend{
+        file = file_path,
+    }
    local ok, stored

    -- File being absent and returning an empty table is a use case,
@@ -57,7 +59,7 @@ function LuaDefaults:open(path)
        error("Failed reading " .. defaults_path)
    end

-    return setmetatable(new, {__index = LuaDefaults})
+    return new
 end

 --- Reads a setting, optionally initializing it to a default.
@@ -161,11 +163,10 @@ function LuaDefaults:flush()
    if not self.file then return end
    local directory_updated = false
    if lfs.attributes(self.file, "mode") == "file" then
-        -- As an additional safety measure (to the ffiutil.fsync* calls
-        -- used below), we only backup the file to .old when it has
-        -- not been modified in the last 60 seconds. This should ensure
-        -- in the case the fsync calls are not supported that the OS
-        -- may have itself sync'ed that file content in the meantime.
+        -- As an additional safety measure (to the ffiutil.fsync* calls used below),
+        -- we only backup the file to .old when it has not been modified in the last 60 seconds.
+        -- This should ensure in the case the fsync calls are not supported
+        -- that the OS may have itself sync'ed that file content in the meantime.
        local mtime = lfs.attributes(self.file, "modification")
        if mtime < os.time() - 60 then
            os.rename(self.file, self.file .. ".old")
--- a/frontend/luasettings.lua
+++ b/frontend/luasettings.lua
@@ -9,16 +9,19 @@ local logger = require("logger")

 local LuaSettings = {}

-function LuaSettings:new(o)
+function LuaSettings:extend(o)
    o = o or {}
    setmetatable(o, self)
    self.__index = self
    return o
 end
+-- NOTE: Instances are created via open, so we do *NOT* implement a new method, to avoid confusion.

 --- Opens a settings file.
 function LuaSettings:open(file_path)
-    local new = {file=file_path}
+    local new = LuaSettings:extend{
+        file = file_path,
+    }
    local ok, stored

    -- File being absent and returning an empty table is a use case,
@@ -41,13 +44,13 @@ function LuaSettings:open(file_path)
        end
    end

-    return setmetatable(new, {__index = LuaSettings})
+    return new
 end

--- @todo DocSettings can return a LuaSettings to use following awesome features.
 function LuaSettings:wrap(data)
-    local new = {data = type(data) == "table" and data or {}}
-    return setmetatable(new, {__index = LuaSettings})
+    return self:extend{
+        data = type(data) == "table" and data or {},
+    }
 end

 --[[--Reads child settings.
@@ -66,7 +69,7 @@ end
    -- result "b"
 ]]
 function LuaSettings:child(key)
-    return LuaSettings:wrap(self:readSetting(key))
+    return self:wrap(self:readSetting(key))
 end

 --[[-- Reads a setting, optionally initializing it to a default.
@@ -251,11 +254,10 @@ function LuaSettings:flush()
    if not self.file then return end
    local directory_updated = false
    if lfs.attributes(self.file, "mode") == "file" then
-        -- As an additional safety measure (to the ffiutil.fsync* calls
-        -- used below), we only backup the file to .old when it has
-        -- not been modified in the last 60 seconds. This should ensure
-        -- in the case the fsync calls are not supported that the OS
-        -- may have itself sync'ed that file content in the meantime.
+        -- As an additional safety measure (to the ffiutil.fsync* calls used below),
+        -- we only backup the file to .old when it has not been modified in the last 60 seconds.
+        -- This should ensure in the case the fsync calls are not supported
+        -- that the OS may have itself sync'ed that file content in the meantime.
        local mtime = lfs.attributes(self.file, "modification")
        if mtime < os.time() - 60 then
            os.rename(self.file, self.file .. ".old")
--- a/frontend/pluginloader.lua
+++ b/frontend/pluginloader.lua
@@ -89,7 +89,7 @@ function PluginLoader:loadPlugins()
    if type(plugins_disabled) ~= "table" then
        plugins_disabled = {}
    end
-    --disable obsolete plugins
+    -- disable obsolete plugins
    for element in pairs(OBSOLETE_PLUGINS) do
        plugins_disabled[element] = true
    end
--- a/frontend/pluginshare.lua
+++ b/frontend/pluginshare.lua
@@ -1,5 +1,6 @@
-- PluginShare is a table for plugins to exchange data between each other. Plugins should maintain
-- their own protocols.
+-- PluginShare is a table for plugins to exchange data between each other.
+-- It is a singleton, which will persist across views (and, as such, across plugins lifecycle).
+-- Plugins should maintain their own protocols.
 return {
    backgroundJobs = {},
 }
--- a/frontend/readhistory.lua
+++ b/frontend/readhistory.lua
@@ -9,6 +9,7 @@ local realpath = ffiutil.realpath

 local history_file = joinPath(DataStorage:getDataDir(), "history.lua")

+-- This is a singleton
 local ReadHistory = {
    hist = {},
    last_read_time = 0,
@@ -70,7 +71,6 @@ local function timeFirstOrdering(l, r)
 end

 function ReadHistory:_indexing(start)
-    assert(self ~= nil)
    --- @todo (Hzj_jie): Use binary search to find an item when deleting it.
    for i = start, #self.hist, 1 do
        self.hist[i].index = i
@@ -78,7 +78,6 @@ function ReadHistory:_indexing(start)
 end

 function ReadHistory:_sort()
-    assert(self ~= nil)
    local autoremove_deleted_items_from_history =
        not G_reader_settings:nilOrFalse("autoremove_deleted_items_from_history")
    if autoremove_deleted_items_from_history then
@@ -98,7 +97,6 @@ end
 -- Reduces total count in hist list to a reasonable number by removing last
 -- several items.
 function ReadHistory:_reduce()
-    assert(self ~= nil)
    while #self.hist > 500 do
        table.remove(self.hist, #self.hist)
    end
@@ -106,7 +104,6 @@ end

 -- Flushes current history table into file.
 function ReadHistory:_flush()
-    assert(self ~= nil)
    local content = {}
    for _, v in ipairs(self.hist) do
        table.insert(content, {
@@ -115,15 +112,16 @@ function ReadHistory:_flush()
        })
    end
    local f = io.open(history_file, "w")
-    f:write("return " .. dump(content) .. "\n")
-    ffiutil.fsyncOpenedFile(f) -- force flush to the storage device
-    f:close()
+    if f then
+        f:write("return " .. dump(content) .. "\n")
+        ffiutil.fsyncOpenedFile(f) -- force flush to the storage device
+        f:close()
+    end
 end

 --- Reads history table from file.
 -- @treturn boolean true if the history_file has been updated and reloaded.
 function ReadHistory:_read(force_read)
-    assert(self ~= nil)
    local history_file_modification_time = lfs.attributes(history_file, "modification")
    if history_file_modification_time == nil
            or (not force_read and (history_file_modification_time <= self.last_read_time)) then
@@ -142,7 +140,6 @@ end

 -- Reads history from legacy history folder
 function ReadHistory:_readLegacyHistory()
-    assert(self ~= nil)
    local history_dir = DataStorage:getHistoryDir()
    for f in lfs.dir(history_dir) do
        local path = joinPath(history_dir, f)
@@ -162,7 +159,6 @@ function ReadHistory:_readLegacyHistory()
 end

 function ReadHistory:_init()
-    assert(self ~= nil)
    self:reload()
 end

@@ -199,7 +195,6 @@ function ReadHistory:getPreviousFile(current_file)
 end

 function ReadHistory:getFileByDirectory(directory, recursive)
-    assert(self ~= nil)
    local real_path = realpath(directory)
    for i=1, #self.hist do
        local ipath = realpath(ffiutil.dirname(self.hist[i].file))
@@ -232,7 +227,6 @@ function ReadHistory:fileSettingsPurged(path)
 end

 function ReadHistory:clearMissing()
-    assert(self ~= nil)
    for i = #self.hist, 1, -1 do
        if self.hist[i].file == nil or lfs.attributes(self.hist[i].file, "mode") ~= "file" then
            self:removeItem(self.hist[i], i)
@@ -242,7 +236,6 @@ function ReadHistory:clearMissing()
 end

 function ReadHistory:removeItemByPath(path)
-    assert(self ~= nil)
    for i = #self.hist, 1, -1 do
        if self.hist[i].file == path then
            self:removeItem(self.hist[i])
@@ -253,7 +246,6 @@ function ReadHistory:removeItemByPath(path)
 end

 function ReadHistory:updateItemByPath(old_path, new_path)
-    assert(self ~= nil)
    for i = #self.hist, 1, -1 do
        if self.hist[i].file == old_path then
            self.hist[i].file = new_path
@@ -273,7 +265,6 @@ function ReadHistory:updateItemByPath(old_path, new_path)
 end

 function ReadHistory:removeItem(item, idx)
-    assert(self ~= nil)
    table.remove(self.hist, item.index or idx)
    os.remove(DocSettings:getHistoryPath(item.file))
    self:_indexing(item.index or idx)
@@ -282,7 +273,6 @@ function ReadHistory:removeItem(item, idx)
 end

 function ReadHistory:addItem(file, ts)
-    assert(self ~= nil)
    if file ~= nil and lfs.attributes(file, "mode") == "file" then
        local now = ts or os.time()
        table.insert(self.hist, 1, buildEntry(now, file))
@@ -303,7 +293,6 @@ end
 --- Reloads history from history_file.
 -- @treturn boolean true if history_file has been updated and reload happened.
 function ReadHistory:reload(force_read)
-    assert(self ~= nil)
    if self:_read(force_read) then
        self:_readLegacyHistory()
        self:_sort()
--- a/frontend/socketutil.lua
+++ b/frontend/socketutil.lua
@@ -90,9 +90,6 @@ socketutil.SINK_TIMEOUT_CODE    = "sink timeout" -- from our own socketutil

 -- NOTE: Use os.time() for simplicity's sake (we don't really need subsecond precision).
 --       LuaSocket itself is already using gettimeofday anyway (although it does the maths, like ffi/util's getTimestamp).
--       Proper etiquette would have everyone using clock_gettime(CLOCK_MONOTONIC) for this kind of stuff,
--       but it's a tad more annoying to use because it's stuffed in librt in old glibc versions,
--       and I have no idea what macOS & Android do with it (but it is POSIX). Plus, win32.
 --- Custom version of `ltn12.sink.table` that honors total_timeout
 function socketutil.table_sink(t)
    if socketutil.total_timeout < 0 then
--- a/frontend/ui/data/keyboardlayouts/ko_KR_helper.lua
+++ b/frontend/ui/data/keyboardlayouts/ko_KR_helper.lua
@@ -213,7 +213,7 @@ local HgFSM = {
    final = nil,

    fsm_state = nil,
-    fsm_prev_states = {},
+    fsm_prev_states = nil, -- array

    do_not_del_in_medial = false,

--- a/frontend/ui/data/keyboardlayouts/zh_ime.lua
+++ b/frontend/ui/data/keyboardlayouts/zh_ime.lua
@@ -48,7 +48,7 @@ end

 local _stack
 local IME = {
-    code_map = {},
+    code_map = nil, -- hash, mandatory
    key_map = nil, -- input key to code map
    keys_string = "abcdefghijklmnopqrstuvwxyz",
    iter_map = nil, -- next code when using wildcard
@@ -351,4 +351,4 @@ function IME:wrappedAddChars(inputbox, char)
    end
 end

-return IME
+return IME
--- a/frontend/ui/hook_container.lua
+++ b/frontend/ui/hook_container.lua
@@ -15,18 +15,15 @@ function HookContainer:new(o)
 end

 function HookContainer:_assertIsValidName(name)
-    assert(self ~= nil)
    assert(type(name) == "string")
    assert(string.len(name) > 0)
 end

 function HookContainer:_assertIsValidFunction(func)
-    assert(self ~= nil)
    assert(type(func) == "function" or type(func) == "table")
 end

 function HookContainer:_assertIsValidFunctionOrNil(func)
-    assert(self ~= nil)
    if func == nil then return end
    self:_assertIsValidFunction(func)
 end
--- a/frontend/ui/message/filemessagequeue.lua
+++ b/frontend/ui/message/filemessagequeue.lua
@@ -5,7 +5,7 @@ local _ = require("ffi/zeromq_h")
 local czmq = ffi.load("libs/libczmq.so.1")
 local filemq = ffi.load("libs/libfmq.so.1")

-local FileMessageQueue = MessageQueue:new{
+local FileMessageQueue = MessageQueue:extend{
    client = nil,
    server = nil,
 }
--- a/frontend/ui/message/messagequeue.lua
+++ b/frontend/ui/message/messagequeue.lua
@@ -7,10 +7,15 @@ local czmq = ffi.load("libs/libczmq.so.1")

 local MessageQueue = {}

-function MessageQueue:new(o)
-    o = o or {}
+function MessageQueue:extend(subclass_prototype)
+    local o = subclass_prototype or {}
    setmetatable(o, self)
    self.__index = self
+    return o
+end
+
+function MessageQueue:new(o)
+    o = self:extend(o)
    if o.init then o:init() end
    self.messages = {}
    return o
--- a/frontend/ui/message/streammessagequeue.lua
+++ b/frontend/ui/message/streammessagequeue.lua
@@ -7,7 +7,7 @@ local zmq = ffi.load("libs/libzmq.so.4")
 local czmq = ffi.load("libs/libczmq.so.1")
 local C = ffi.C

-local StreamMessageQueue = MessageQueue:new{
+local StreamMessageQueue = MessageQueue:extend{
    host = nil,
    port = nil,
 }
--- a/frontend/ui/network/networklistener.lua
+++ b/frontend/ui/network/networklistener.lua
@@ -1,15 +1,15 @@
 local BD = require("ui/bidi")
 local Device = require("device")
 local Event = require("ui/event")
+local EventListener = require("ui/widget/eventlistener")
 local InfoMessage = require("ui/widget/infomessage")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local NetworkMgr = require("ui/network/manager")
 local UIManager = require("ui/uimanager")
 local logger = require("logger")
 local _ = require("gettext")
 local T = require("ffi/util").template

-local NetworkListener = InputContainer:new{}
+local NetworkListener = EventListener:extend{}

 function NetworkListener:onToggleWifi()
    if not NetworkMgr:isWifiOn() then
--- a/frontend/ui/plugin/switch_plugin.lua
+++ b/frontend/ui/plugin/switch_plugin.lua
@@ -11,7 +11,7 @@ local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local logger = require("logger")
 local _ = require("gettext")

-local SwitchPlugin = WidgetContainer:new()
+local SwitchPlugin = WidgetContainer:extend{}

 function SwitchPlugin:extend(o)
    o = o or {}
--- a/frontend/ui/rendertext.lua
+++ b/frontend/ui/rendertext.lua
@@ -6,17 +6,12 @@ local bit = require("bit")
 local Font = require("ui/font")
 local Cache = require("cache")
 local Blitbuffer = require("ffi/blitbuffer")
-local Device = require("device")
 local logger = require("logger")

 local band = bit.band
 local bor = bit.bor
 local lshift = bit.lshift

-if Device.should_restrict_JIT then
-    jit.off(true, true)
-end
-
 --[[
@TODO: all these functions should probably be methods on Face objects
 ]]--
--- a/frontend/ui/screensaver.lua
+++ b/frontend/ui/screensaver.lua
@@ -54,12 +54,14 @@ end

 local Screensaver = {
    screensaver_provider = {
+        gif  = true,
        jpg  = true,
        jpeg = true,
        png  = true,
-        gif  = true,
+        svg  = true,
        tif  = true,
        tiff = true,
+        webp = true,
    },
    default_screensaver_message = _("Sleeping"),
 }
--- a/frontend/ui/uimanager.lua
+++ b/frontend/ui/uimanager.lua
@@ -16,7 +16,7 @@ local Screen = Device.screen

 local DEFAULT_FULL_REFRESH_COUNT = 6

-- there is only one instance of this
+-- This is a singleton
 local UIManager = {
    -- trigger a full refresh when counter reaches FULL_REFRESH_COUNT
    FULL_REFRESH_COUNT =
@@ -60,6 +60,7 @@ function UIManager:init()
    }
    self.poweroff_action = function()
        self._entered_poweroff_stage = true
+        logger.info("Powering off the device...")
        Device.orig_rotation_mode = Device.screen:getRotationMode()
        self:broadcastEvent(Event:new("Close"))
        Screen:setRotationMode(Screen.ORIENTATION_PORTRAIT)
@@ -74,6 +75,7 @@ function UIManager:init()
    end
    self.reboot_action = function()
        self._entered_poweroff_stage = true
+        logger.info("Rebooting the device...")
        Device.orig_rotation_mode = Device.screen:getRotationMode()
        self:broadcastEvent(Event:new("Close"))
        Screen:setRotationMode(Screen.ORIENTATION_PORTRAIT)
--- a/frontend/ui/widget/bboxwidget.lua
+++ b/frontend/ui/widget/bboxwidget.lua
@@ -12,7 +12,7 @@ local Screen = Device.screen
 local Size = require("ui/size")
 local UIManager = require("ui/uimanager")

-local BBoxWidget = InputContainer:new{
+local BBoxWidget = InputContainer:extend{
    page_bbox = nil,
    screen_bbox = nil,
    linesize = Size.line.thick,
--- a/frontend/ui/widget/bookmapwidget.lua
+++ b/frontend/ui/widget/bookmapwidget.lua
@@ -23,6 +23,7 @@ local UIManager = require("ui/uimanager")
 local VerticalGroup = require("ui/widget/verticalgroup")
 local VerticalSpan = require("ui/widget/verticalspan")
 local Widget = require("ui/widget/widget")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local Input = Device.input
 local Screen = Device.screen
 local logger = require("logger")
@@ -30,7 +31,7 @@ local util = require("util")
 local _ = require("gettext")

 -- BookMapRow (reused by PageBrowserWidget)
-local BookMapRow = InputContainer:new{
+local BookMapRow = WidgetContainer:extend{
    width = nil,
    height = nil,
    pages_frame_border = Size.border.default,
@@ -102,7 +103,7 @@ end

 function BookMapRow:init()
    local _mirroredUI = BD.mirroredUILayout()
-    self.dimen = Geom:new{ w = self.width, h = self.height }
+    self.dimen = Geom:new{ x = 0, y = 0, w = self.width, h = self.height }

    -- Keep one span_height under baseline (frame bottom border) for indicators (current page, bookmarks)
    self.pages_frame_height = self.height - self.span_height
@@ -517,7 +518,7 @@ function BookMapRow:paintTo(bb, x, y)
 end

 -- BookMapWidget: shows a map of content, including TOC, boomarks, read pages, non-linear flows...
-local BookMapWidget = InputContainer:new{
+local BookMapWidget = InputContainer:extend{
    title = _("Book map"),
    -- Focus page: show the BookMapRow containing this page
    -- in the middle of screen
@@ -538,6 +539,8 @@ function BookMapWidget:init()

    -- Compute non-settings-dependant sizes and options
    self.dimen = Geom:new{
+        x = 0,
+        y = 0,
        w = Screen:getWidth(),
        h = Screen:getHeight(),
    }
--- a/frontend/ui/widget/bookstatuswidget.lua
+++ b/frontend/ui/widget/bookstatuswidget.lua
@@ -32,37 +32,32 @@ local T = require("ffi/util").template
 local stats_book = {}

 --[[
--Save into sdr folder addtional section
+-- Stored in the sidecar metadata, in a dedicated table:
 ["summary"] = {
    ["rating"] = 5,
    ["note"] = "Some text",
    ["status"] = "Reading"
    ["modified"] = "24.01.2016"
 },]]
-local BookStatusWidget = FocusManager:new{
+local BookStatusWidget = FocusManager:extend{
    padding = Size.padding.fullscreen,
    settings = nil,
    thumbnail = nil,
    props = nil,
-    star = {},
-    summary = {
-        rating = nil,
-        note = nil,
-        status = "",
-        modified = "",
-    },
+    star = nil, -- Button
+    summary = nil, -- hash
 }

 function BookStatusWidget:init()
    self.layout = {}
+    -- What a blank, full summary table should look like
+    local new_summary = {
+        rating = nil,
+        note = nil,
+        status = "",
+        modified = "",
+    }
    if self.settings then
-        -- What a blank, full summary table should look like
-        local new_summary = {
-            rating = nil,
-            note = nil,
-            status = "",
-            modified = "",
-        }
        local summary = self.settings:readSetting("summary")
        -- Check if the summary table we get is a full one, or a minimal one from CoverMenu...
        if summary then
@@ -77,6 +72,8 @@ function BookStatusWidget:init()
        else
            self.summary = new_summary
        end
+    else
+        self.summary = new_summary
    end
    self.total_pages = self.ui.document:getPageCount()
    stats_book = self:getStats()
--- a/frontend/ui/widget/button.lua
+++ b/frontend/ui/widget/button.lua
@@ -35,7 +35,7 @@ local logger = require("logger")

 local DGENERIC_ICON_SIZE = G_defaults:readSetting("DGENERIC_ICON_SIZE")

-local Button = InputContainer:new{
+local Button = InputContainer:extend{
    text = nil, -- mandatory (unless icon is provided)
    text_func = nil,
    icon = nil,
--- a/frontend/ui/widget/buttondialog.lua
+++ b/frontend/ui/widget/buttondialog.lua
@@ -12,7 +12,7 @@ local UIManager = require("ui/uimanager")
 local _ = require("gettext")
 local Screen = require("device").screen

-local ButtonDialog = InputContainer:new{
+local ButtonDialog = InputContainer:extend{
    buttons = nil,
    tap_close_callback = nil,
    alpha = nil, -- passed to MovableContainer
--- a/frontend/ui/widget/buttondialogtitle.lua
+++ b/frontend/ui/widget/buttondialogtitle.lua
@@ -16,7 +16,7 @@ local VerticalSpan = require("ui/widget/verticalspan")
 local _ = require("gettext")
 local Screen = Device.screen

-local ButtonDialogTitle = InputContainer:new{
+local ButtonDialogTitle = InputContainer:extend{
    title = nil,
    title_align = nil,
    title_face = Font:getFace("x_smalltfont"),
--- a/frontend/ui/widget/buttonprogresswidget.lua
+++ b/frontend/ui/widget/buttonprogresswidget.lua
@@ -11,7 +11,7 @@ local UIManager = require("ui/uimanager")
 local _ = require("gettext")
 local Screen = Device.screen

-local ButtonProgressWidget = FocusManager:new{
+local ButtonProgressWidget = FocusManager:extend{
    width = Screen:scaleBySize(216),
    height = Size.item.height_default,
    padding = Size.padding.small,
--- a/frontend/ui/widget/buttontable.lua
+++ b/frontend/ui/widget/buttontable.lua
@@ -10,7 +10,7 @@ local VerticalSpan = require("ui/widget/verticalspan")
 local Geom = require("ui/geometry")
 local Screen = Device.screen

-local ButtonTable = FocusManager:new{
+local ButtonTable = FocusManager:extend{
    width = nil,
    buttons = {
        {
--- a/frontend/ui/widget/checkbutton.lua
+++ b/frontend/ui/widget/checkbutton.lua
@@ -27,7 +27,7 @@ local UIManager = require("ui/uimanager")
 local VerticalGroup = require("ui/widget/verticalgroup")
 local VerticalSpan = require("ui/widget/verticalspan")

-local CheckButton = InputContainer:new{
+local CheckButton = InputContainer:extend{
    callback = nil,
    hold_callback = nil,
    checkable = true, -- empty space when false
--- a/frontend/ui/widget/checkmark.lua
+++ b/frontend/ui/widget/checkmark.lua
@@ -17,11 +17,11 @@ Example:
 local BD = require("ui/bidi")
 local Blitbuffer = require("ffi/blitbuffer")
 local Font = require("ui/font")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local OverlapGroup = require("ui/widget/overlapgroup")
 local TextWidget = require("ui/widget/textwidget")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")

-local CheckMark = InputContainer:new{
+local CheckMark = WidgetContainer:extend{
    checkable = true,
    checked = false,
    enabled = true,
--- a/Show More
+++ b/Show More