3.91.0 (unstable):
Distro packagers should probably not package this yet.

Gdk:
* Improve Gdk::Event, creating a class hierarchy.
  (Mark Vender, Kjell Ahlstedt) Bug #135978
* Cursor: Change CursorType to Cursor::Type.
  (Murray Cumming)
* Device: Change DeviceType to Cursor::Type.
  (Murray Cumming)
* Pixbuf:
  - Remove AlphaMode enum.
  - Change PixbufRotation to Pixbuf::Rotation.
  (Murray Cumming)
* Seat: Change SeatCapabilities to Seat::Capabilities.
  (Murray Cumming)
* Visual: Change VisualType to Visual::Type.
  (Murray Cumming)
* Window:
  - Change WindowHints to Window::Hints.
  - Change WindowTypeHint to Window::TypeHint.
  - Change WindowType to Window::Type.
  - Change WindowState to Window::State.
  (Murray Cumming)

Gtk:
* Assistant: Change AssistantPageType to Assistant::PageType.
  (Murray Cumming)
* Box: pack_start/pack_end(): Reimplement with new GTK+ API.
  (GtkWidget halign and hexpand properties.
  The gtk_box_pack_start() and gtk_box_pack_end() functions no longer
  have the expand and fill arguments.
  We might remove these parameters later too.
  Be careful that the default behaviour of pack_start/pack_end() has now
  changed.
  - Make PackOptions an enum class, for stricter type checking.
  (Murray Cumming)
* Builder::get_widget_derived(): Make this static.
  To avoid the need to create a shared_ptr to this.
  (Murray Cumming) Bug #755037
* ButtonBox: Remove apparently-useless BUTTONBOX_DEFAULT_SPACING.
  (Murray Cumming)
* Application: Change ApplicationInhibitFlags to Application::InhibitFlags.
  (Murray Cumming)
* Calendar: Change CalendarDisplayOptions to Calendar::Display::Options.
  (Murray Cumming)
* CellRendererAccel: Change CellRendererAccelMode to CellRendererAccel::Mode.
  (Murray Cumming)
* CssSection: Change CssSectionType to CssSection::Typewq.
  (Murray Cumming)
* Container:
  - forall_vfunc(): Remove include_internals parameter.
  - Remove set_focus_child(), get_focus_child(), etc.
  (Murray Cumming)
* Entry: Change EntryIconPosition to Entry::IconPosition.
  (Murray Cumming)
* FileFilter: Change FileFilterFlags to FileFilter::Flags.
  (Murray Cumming)
* FileChooser:
  - Change FileChooserConfirmation to FileChooser::Confirmation.
  - Change FileChooserAction to FileChooser::Action.
  (Murray Cumming)
* IconView: change IconViewDropPosition to IconView::DropPosition.
  (Murray Cumming)
* Image: Change ImageType to Image::Type.
  (Murray Cumming)
* Label: Remove get/set_angle() and property.
  (Murray Cumming)
* LevelBar: Change LevelBarMode to LevelBar::Mode.
  (Murray Cumming)
* Notebook: Remove NotebookTab enum.
  (Murray Cumming)
* Popover: Change PopoverConstraint to Popover::Constraint.
  (Murray Cumming)
* PrintOperation:
  - Change PrintOperationAction to PrintOperation::Action.
  - Change PrintOperationResult to PrintOperation::Result.
  (Murray Cumming)
* Range: Derive from (and implement) Orientable.
  (Muray Cumming) Bug #781655 (Daniel Boles)
* RecentFilter: Change RecentFilterFlags to RecentFilter::Flags.
  (Murray Cumming)
* Scrollable: Change ScrollablePolicy to Scrollable::Policy.
  (Murray Cumming)
* ShortcutsShortcut: Derive directly from Widget.
  (Kjell Ahlstedt)
* SizeGroup: Rename SizeGroupMode enum to SizeGroup::Mode.
  (Murray Cumming)
* SpinButton:
  - Change SpinButtonUpdatePolicy to SpinButton::UpdatePolicy.
  - Move INPUT_ERROR constant into class.
  (Murray Cumming)
* TextConstIter (TextModel::const_iterator): Add a default constructor.
  (Murray Cumming)
* TextMark: Avoid creating a RefPtr to this.
  By adding a private TextBuffer::get_iter_at_mark()
  (Murray Cumming) Bug #755037#c21
* TreeModel: Change TreeModelFlags to TreeModel::Flags.
  (Murray Cumming)
* TreeView:
  - Change TreeViewGridLines to GridLines.
  - Change TreeViewDropPosition to TreeView::DropPosition.
  (Murray Cumming)
* TreeViewColumn: Change TreeViewColumnSizing to TreeViewColumn::Sizing.
  (Murray Cumming)
* Widget:
  - Remove get_preferred_width() etc.
  (Kjell Ahlstedt)
  - Remove get/set_center_widget().
  (Murray Cumming)
* Window:
  - Remove get/set_hide_titlebar_when_maximized().
  - Remove has_toplevel_focus() and property.
  (Murray Cumming)

Documentation:
* Gtk::CellLayout: Improve docs of get_first_cell() funcs.
  (Daniel Boles)
* Gtk::TreeModel: Improve docs of foreach*() functions.
  (Daniel Boles)
* Gdk, Gtk: Update documentation of in-class enums.
  (Kjell Ahlstedt)
* Demos:
  - Fix make check after changes in Glib::SignalProxy::connect()
  (Kjell Ahlstedt) Bug 126213
  - Adapt to changed Box::pack_start/pack_end() behaviour.
  For instance: Specify EXPAND_WIDGET, where we previously
  used the default value.
  (Murray Cumming)
* Builder demo: Remove "expand" child property from the .ui file
  Because it has been removed from GtkBox. Expand the ScrolledWindow.
  (Kjell Ahlstedt)

Build:
* Adapt to cairomm and glibmm enum changes.
  (Murray Cumming)
* Adapt dynamic casts for RefPtr as std::shared_ptr.
  (Murray Cumming)
* Visual Studio builds: Update glibmm ABI version.
  (Chun-wei Fan)