Happy new year! & comments

Comments: fixed missing line in the "how a simple rendering function may look like" section (#2258)

Error recovery: Extraneous/undesired calls to End() are now being caught by an assert in the End() function itself at the call site (instead of being reported in EndFrame). Past the assert, they don't lead to crashes any more. Missing calls to End(), pass the assert, should not lead to crashes any more, nor to the fallback/debug window appearing on screen. (#1651).

Tweaked asserts

Build fix for master.

Examples: SDL: Avoid testing for SDL_GetKeyboardFocus() on Android and iOS (like Emscripten). (#421)

Examples: Setting up style before bindings, so in complex binding (vulkan/dx12) it isn't miles away from the context creation.

Made it illegal to call Begin("") with an empty string. This somehow accidentally worked before but had various undesirable side-effect as the window would have ID zero. In particular it is causing problems in viewport/docking branches.

IO: Realigned all fields, very minor comments change. This is nearly a no-op if you don't ignore Spaces.

IO: Added BackendPlatformUserData, BackendRendererUserData, BackendLanguageUserData void* for storage use by back-ends. (#2004 + for cimgui)

Changed ImGuiCol_ChildBg to (0,0,0,0) in Dark style instead of (1,1,1,0), to match other styles. Shouldn't have any effect for the end-user.

Fixed using SetNextWindowPos() on a child window (which wasn't really documented) position the cursor as expected in the parent window, so there is no mismatch between the layout in parent and the position of the child window. Demo tweak and adding some child window stuff

Various user-facing comments

Tidying up README, moved entries to FAQ, updated screenshots, removed comma in title.

Fix merge issue on master.

Window, Focus, Popup: Fixed an issue where closing a popup by clicking another window with the _NoMove flag would refocus the parent window of the popup instead of the newly clicked window.

Moved setting up NavHideHighlightOneFrame from lower-level ClosePopupToLevel() to CloseCurrentPopup() with an explanation. (Followup on 68d3e13)

Docs: various updates, rewording, clarifying the purpose of a PR.

Internals: Popups: Renamed CurrentPopupStack to BeginPopupStack which is much less ambiguous.

Internals: Popups: EndMenu() calls ClosePopupToLevel(g.CurrentPopupStack.Size) which is more correct.

Internals: Popup related comments. Renamed the misleading internal ClosePopup() function. Added bool* test to BeginPopupModal in demo.

Tests: Changed prototype of ImGuiTestEngineHook_ItemAdd to match functions called in same spot. Made ButtonBehavior submit fallback item info if ItemAdd() was not called (for resize grips, resize borders, scrollbar, columns, etc.)

Comments, minor tweaks.

Tabs: Fixed support for drag and drop ImGuiButtonFlags_PressedOnDragDropHold. (#261) incorrectly missing from the merge from Docking branch.

Internals: Windows hidden with HiddenFramesRegular (but NOT HiddenFramesForResize) preserve their SizeContents, so restoring a auto-resize window after it's been hidden by tabs won't reset its size for a frame. Arguable. Let's see how it goes. (Followup to b48e295)

Contents size is preserved while a window collapsed. Fix auto-resizing window losing their size for one frame when uncollapsed.

Demo: Using Tabs in Style Editor and Simple Layout example. + Adding missing early out in About and Documents examples.

BeginTabBar: Fix to push the expected ID into the ID stack (instead of a hash's hash). (#261)

Demo: Fix collateral damage of 54a60aa

Added BETA api for Tab Bar/Tabs widgets. (#261, #351) (merged this feature from the from Docking branch so it can be used earlier as as standalone feature) ...

- Added BeginTabBar(), EndTabBar(), BeginTabItem(), EndTabItem(), SetTabItemClosed() API.
- Added ImGuiTabBarFlags flags for BeginTabBar().
- Added ImGuiTabItemFlags flags for BeginTabItem().
- Style: Added ImGuiCol_Tab, ImGuiCol_TabHovered, ImGuiCol_TabActive, ImGuiCol_TabUnfocused, ImGuiCol_TabUnfocusedActive colors.
- Demo: Added Layout->Tabs demo code.
- Demo: Added "Documents" example app showcasing possible use for tabs.