Relative to the XKB 1.1 specification implemented in current X servers, xkbcommon has removed support for some parts of the specification which introduced unnecessary complications. Many of these removals were in fact not implemented, or half-implemented at best, as well as being totally unused in the standard dataset.

Notable removals:

• geometry support
  • there were very few geometry definitions available, and while xkbcommon was responsible for parsing this insanely complex format, it never actually did anything with it
  • hopefully someone will develop a companion library which supports keyboard geometries in a more useful format
• KcCGST (keycodes/compat/geometry/symbols/types) API
  • use RMLVO instead; KcCGST is now an implementation detail
  • including pre-defined keymap files
• XKM support
  • may come in an optional X11 support/compatibility library
• around half of the interpret actions
  • pointer device, message and redirect actions in particular
• non-virtual modifiers
  • core and virtual modifiers have been collapsed into the same namespace, with a 'significant' flag that largely parallels the core/virtual split
• radio groups
  • completely unused in current keymaps, never fully implemented
• overlays
  • almost completely unused in current keymaps
• key behaviors
  • used to implement radio groups and overlays, and to deal with things like keys that physically lock; unused in current keymaps
• indicator behaviours such as LED-controls-key
  • the only supported LED behaviour is key-controls-LED; again this was never really used in current keymaps

On the other hand, some features and extensions were added.

Notable additions:

• 32-bit keycodes
• extended number of modifiers (planned)
• extended number of groups (planned)
• multiple keysyms per level
  • this requires incompatible dataset changes, such that X11 would not be able to parse these

Compose support

Relative to the standard implementation in libX11 (described in the Compose(5) man-page), some features are not supported:

• the (! MODIFIER) syntax
• using modifier keysyms in Compose sequences
• several interactions with Braille keysyms