kc3-lang/libxkbcommon/doc/compatibility.md

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  Date : 2025-07-01T14:52:11
  

  Add support for all level indices to LevelN constants
  
  Note that serialization must use numbers instead of names for levels > 8,
  to ensure backward compatibility.
  

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• doc/compatibility.md

• # XKB Compatibility {#xkbcommon-compatibility}
  
  @tableofcontents{html:2}
  
  This page presents the differences between the [XKB 1.0 specification][XKB Protocol]
  implemented in current X servers and its implementation in libxkbcommon.
  
  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 keyboard layout database, [xkeyboard-config].
  
  On the other hand, xkbcommon has notable additions that lift hard-coded
  limitation of the [X11 Protocol].
  
  @todo This page is work in progress. It aims to be exhaustive.
  Please [report any issue](https://github.com/xkbcommon/libxkbcommon/issues).
  
  [X11 Protocol]: https://www.x.org/releases/current/doc/xproto/x11protocol.html#Keyboards
  [XKB Protocol]: https://www.x.org/releases/current/doc/kbproto/xkbproto.html
  [xkeyboard-config]: https://gitlab.freedesktop.org/xkeyboard-config/xkeyboard-config
  
  ## Keymap support {#keymap-support}
  
  ### General features
  
  <table>
  <caption>Keymap features compatibility table</caption>
  <thead>
  <tr>
  <th>Feature</th>
  <th>X11</th>
  <th>xkbcommon (v1 format)</th>
  <th>xkbcommon (v2 format)</th>
  </tr>
  </thead>
  <tbody>
  <!-- Additions -->
  <tr>
  <th>Wayland support</th>
  <td>
  <details>
  <summary>❌️ No support</summary>
  Wayland support requires the XWayland compatibility layer.
  </details>
  </td>
  <td colspan="2">
  <details>
  <summary>✅ Full support</summary>
  libxkbcommon is the *reference* implementation of the keyboard keymap handling
  (parsing/serializing, state) for Wayland.
  </details>
  </td>
  </tr>
  <tr>
  <th>User configuration</th>
  <td>
  <details>
  <summary>❌️ No support</summary>
  Layout database path is *hard-coded* in xserver.
  
  `xkbcomp` enable path configuration, but `setxkbmap` support is incomplete.
  </details>
  </td>
  <td colspan="2">
  <details>
  <summary>✅ Full support</summary>
  Multiple layout database path can be used simultaneously, enabling user-space
  configuration.
  
  See @ref user-configuration "" for further information.
  </details>
  </td>
  </tr>
  <tr>
  <th>Extended keycodes</th>
  <td>
  <details>
  <summary>❌️ No support</summary>
  Limited to **8**-bit keycodes.
  </details>
  </td>
  <td colspan="2">
  <details>
  <summary>✅ Full support</summary>
  Support all Linux keycodes using **32**-bit keycodes.
  </details>
  </td>
  </tr>
  <tr>
  <th>Extended key names</th>
  <td>
  <details>
  <summary>❌️ No support</summary>
  Limited to **4**-character names.
  </details>
  </td>
  <td colspan="2">
  <details>
  <summary>✅ Full support</summary>
  Support any key names of any length.
  </details>
  </td>
  </tr>
  <tr>
  <th>Extended number of layouts</th>
  <td>
  <details>
  <summary>❌️ No support</summary>
  Limited to **4** layouts.
  </details>
  </td>
  <td>
  <details>
  <summary>❌️ No support</summary>
  Limited to **4** layouts.
  </details>
  </td>
  <td>
  <details>
  <summary>✅ Full support (since 1.11)</summary>
  Enable up to **32** layouts when using `::XKB_KEYMAP_FORMAT_TEXT_V2`.
  </details>
  </td>
  </tr>
  <tr>
  <th>Unified modifiers</th>
  <td>
  <details>
  <summary>❌️ No support</summary>
  Clear separation between *real* (i.e. core) and *virtual* modifiers.
  </details>
  </td>
  <td colspan="2">
  <details>
  <summary>✅ Full support</summary>
  Real and virtual modifiers have been collapsed into the same namespace, with a
  “significant” flag that largely parallels the core/virtual split.
  
  Real modifiers are predefined modifiers with fixed encoding and considered merely
  as a X11 compatibility feature.
  </details>
  </td>
  </tr>
  <tr>
  <th>Extended modifiers</th>
  <td>
  <details>
  <summary>❌️ No support</summary>
  Limited to up to **8** *independent* modifiers.
  </details>
  </td>
  <td colspan="2">
  <details>
  <summary>✅ Full support</summary>
  Enable up to **32** *independent* modifiers.
  </details>
  </td>
  </tr>
  <tr>
  <th>Canonical virtual modifiers</th>
  <td>
  <details>
  <summary>❌️ No support</summary>
  Virtual modifiers can only mapped to *real* modifiers (8 bits).
  </details>
  </td>
  <td>
  <details>
  <summary>⚠️ Partial support</summary>
  Only if using explicit mapping: e.g. `virtual_modifiers M = 0x100;` if `M` has
  the modifier index 8.
  </details>
  </td>
  <td>
  <details>
  <summary>✅ Full support</summary>
  Virtual modifiers that are not mapped either *explicitly* (using e.g.
  `virtual_modifiers M = …`) or *implicitly* (using `modifier_map` and
  `virtualModifier`) [automatically](@ref auto-modifier-encoding) use to
  their <em>[canonical mapping](@ref canonical-modifier-def)</em>.
  </details>
  </td>
  </tr>
  <tr>
  <th>Multiple keysyms per level</th>
  <td>
  <details>
  <summary>❌️ Parsing only</summary>
  Ignored: fallback to `NoSymbol`.
  </details>
  </td>
  <td colspan="2">
  <details>
  <summary>✅ Full support</summary>
  @todo rationale
  </details>
  </td>
  </tr>
  <tr>
  <th>Multiple actions per level</th>
  <td>
  <details>
  <summary>❌️ No support</summary>
  Parse error.
  </details>
  </td>
  <td>
  <details>
  <summary>⚠️ Parsing & handling, no serialization</summary>
  Currently limited to 1 action for each action type “group” and “modifier”.
  
  @since 1.8: Enable multiple actions per level (parsing, serializing & handling).
  @since 1.11: Serialize to `VoidAction()` for compatibility with X11.
  </details>
  </td>
  <td>
  <details>
  <summary>⚠️ Partial support</summary>
  Currently limited to 1 action for each action type “group” and “modifier”.
  
  @since 1.11
  </details>
  </td>
  </tr>
  <!-- Removals -->
  <tr>
  <th>Geometry @anchor geometry-support</th>
  <td>✅ Full support</td>
  <td colspan="2">
  <details>
  <summary>⚠️ Parsing only</summary>
  
  Rational:
  - There were very few geometry definitions available in [xkeyboard-config], 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, e.g. SVG.
  </details>
  </td>
  </tr>
  <tr>
  <th>Radio groups</th>
  <td>✅ Full support</td><!-- exact status? -->
  <td colspan="2">
  <details>
  <summary>❌️ No support</summary>
  Unused in [xkeyboard-config] layouts.
  </details>
  </td>
  </tr>
  <tr>
  <th>Overlays</th>
  <td>✅ Full support</td>
  <td colspan="2">
  <details>
  <summary>❌️ No support</summary>
  Unused in [xkeyboard-config] layouts.
  </details>
  </td>
  </tr>
  <tr>
  <th>[Key behaviors]</th>
  <td>✅ Full support</td>
  <td colspan="2">
  <details>
  <summary>❌️ No support</summary>
  Used to implement radio groups and overlays, and to deal with things
  like keys that physically lock;
  
  Unused in [xkeyboard-config] layouts.
  </details>
  </td>
  </tr>
  <tr>
  <th>[Indicator behaviors]</th>
  <td>✅ Full support</td>
  <td colspan="2">
  <details>
  <summary>⚠️ Partial support</summary>
  <!-- See commit 6e676cb7 -->
  E.g. LED-controls-key behavior (X11’s `IM_LEDDrivesKB` flag enabled) is not
  supported.
  
  The only supported LED behavior is *key-controls-LED*.
  
  Unused in [xkeyboard-config] layouts.
  </details>
  </td>
  </tr>
  </tbody>
  </table>
  
  [Key behaviors]: https://www.x.org/releases/current/doc/kbproto/xkbproto.html#Key_Behavior
  [Indicator behaviors]: https://www.x.org/releases/current/doc/kbproto/xkbproto.html#:~:text=IM_LEDDrivesKB
  
  
  ### Key actions {#compatibility-key-actions}
  
  <table>
  <caption>Key actions compatibility table</caption>
  <thead>
  <tr>
  <th>Type</th>
  <th>Action</th>
  <th>X11</th>
  <th>xkbcommon (v1 format)</th>
  <th>xkbcommon (v2 format)</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <th rowspan="2">Ineffectual</th>
  <th>`NoAction()`</th>
  <td>✅ Full support</td>
  <td colspan="2">✅ Full support</td>
  </tr>
  <tr>
  <th>`VoidAction()`</th>
  <td>❌️ No support</td>
  <td>⚠️ Parsing only (since 1.10)</td>
  <td>✅ Full support (since 1.11)</td>
  </tr>
  <tr>
  <th rowspan="3">Modifiers</th>
  <th>`SetModifiers()`</th>
  <td>
  <details>
  <summary>⚠️ Partial support</summary>
  - `unlockOnPress` parameter is not supported.
  </details>
  </td>
  <td>
  <details>
  <summary>⚠️ Partial support</summary>
  - `unlockOnPress` parameter is not supported. Use `::XKB_KEYMAP_FORMAT_TEXT_V2`.
  </details>
  </td>
  <td>
  <details>
  <summary>✅ Full support</summary>
  - `unlockOnPress` parameter (since 1.11). See @ref set-mods-action "its documentation"
    for further details.
  </details>
  </td>
  </tr>
  <tr>
  <th>`LatchModifiers()`</th>
  <td>
  <details>
  <summary>⚠️ Partial support</summary>
  - `latchOnPress` parameter is not supported.
  - `unLockOnPress` parameter is not supported.
  </details>
  </td>
  <td>
  <details>
  <summary>⚠️ Partial support</summary>
  - `latchOnPress` parameter is not supported. Use `::XKB_KEYMAP_FORMAT_TEXT_V2`.
  - `unLockOnPress` parameter is not supported. Use `::XKB_KEYMAP_FORMAT_TEXT_V2`.
  </details>
  </td>
  <td>
  <details>
  <summary>✅ Full support</summary>
  - `latchOnPress` parameter (since 1.11). See @ref latch-mods-action "its documentation"
    for further details.
  - `unLockOnPress` parameter (since 1.11). See @ref latch-mods-action "its documentation"
    for further details.
  </details>
  </td>
  </tr>
  <tr>
  <th>`LockModifiers()`</th>
  <td>
  <details>
  <summary>⚠️ Partial support</summary>
  - `unlockOnPress` parameter is not supported.
  </details>
  </td>
  <td>
  <details>
  <summary>⚠️ Partial support</summary>
  - `unlockOnPress` parameter is not supported. Use `::XKB_KEYMAP_FORMAT_TEXT_V2`.
  </details>
  </td>
  <td>
  <details>
  <summary>✅ Full support</summary>
  - `unlockOnPress` parameter (since 1.11). See @ref lock-mods-action "its documentation"
    for further details.
  </details>
  </td>
  </tr>
  <tr>
  <th rowspan="3">Groups</th>
  <th>`SetGroup()`</th>
  <td>✅ Full support</td>
  <td colspan="2">✅ Full support</td>
  </tr>
  <tr>
  <th>`LatchGroup()`</th>
  <td>✅ Full support</td>
  <td colspan="2">✅ Full support</td>
  </tr>
  <tr>
  <th>`LockGroup()`</th>
  <td>
  <details>
  <summary>⚠️ Partial support</summary>
  - `lockOnRelease` parameter is not supported. Use `::XKB_KEYMAP_FORMAT_TEXT_V2`.
  </details>
  </td>
  <td>
  <details>
  <summary>⚠️ Partial support</summary>
  - `lockOnRelease` parameter is not supported. Use `::XKB_KEYMAP_FORMAT_TEXT_V2`.
  </details>
  </td>
  <td>
  <details>
  <summary>✅ Full support</summary>
  - `lockOnRelease` (since 1.11). See @ref lock-group-action "its documentation"
    for further details.
  </details>
  </td>
  </tr>
  <tr>
  <th rowspan="9">Legacy action</th>
  <th>`MovePointer()`</th>
  <td>✅ Full support</td>
  <td colspan="2">⚠️ Parsing and serializing only, no API support</td>
  </tr>
  <tr>
  <th>`PointerButton()`</th>
  <td>✅ Full support</td>
  <td colspan="2">⚠️ Parsing and serializing only, no API support</td>
  </tr>
  <tr>
  <th>`LockPointerButton()`</th>
  <td>✅ Full support</td>
  <td colspan="2">⚠️ Parsing and serializing only, no API support</td>
  </tr>
  <tr>
  <th>`SetPointerDefault()`</th>
  <td>✅ Full support</td>
  <td colspan="2">⚠️ Parsing and serializing only, no API support</td>
  </tr>
  <tr>
  <th>`SetControls()`</th>
  <td>✅ Full support</td>
  <td colspan="2">⚠️ Parsing and serializing only, no API support</td>
  </tr>
  <tr>
  <th>`LockControls()`</th>
  <td>✅ Full support</td>
  <td colspan="2">⚠️ Parsing and serializing only, no API support</td>
  </tr>
  <tr>
  <th>`TerminateServer()`</th>
  <td>✅ Full support</td>
  <td colspan="2">⚠️ Parsing and serializing only, no API support</td>
  </tr>
  <tr>
  <th>`SwitchScreen()`</th>
  <td>✅ Full support</td>
  <td colspan="2">⚠️ Parsing and serializing only, no API support</td>
  </tr>
  <tr>
  <th>`Private()`</th>
  <td>✅ Full support</td>
  <td colspan="2">⚠️ Parsing and serializing only, no API support</td>
  </tr>
  <tr>
  <th rowspan="6">Unsupported legacy action</th>
  <th>`RedirectKey()`</th>
  <td>✅ Full support</td>
  <td colspan="2">❌️ Parsing only</td>
  </tr>
  <tr>
  <th>`ISOLock()`</th>
  <td>✅ Full support</td>
  <td colspan="2">❌️ Parsing only</td>
  </tr>
  <tr>
  <th>`DeviceButton()`</th>
  <td>✅ Full support</td>
  <td colspan="2">❌️ Parsing only</td>
  </tr>
  <tr>
  <th>`LockDeviceButton()`</th>
  <td>✅ Full support</td>
  <td colspan="2">❌️ Parsing only</td>
  </tr>
  <tr>
  <th>`DeviceValuator()`</th>
  <td>✅ Full support</td>
  <td colspan="2">❌️ Parsing only</td>
  </tr>
  <tr>
  <th>`MessageAction()`</th>
  <td>✅ Full support</td>
  <td colspan="2">❌️ Parsing only</td>
  </tr>
  </tbody>
  </table>
  
  
  ### Keymap text format
  
  <table>
  <caption>Keymap text format compatibility table</caption>
  <thead>
  <tr>
  <th>Feature</th>
  <th>X11 (xkbcomp)</th>
  <th>xkbcommon (v1 format)</th>
  <th>xkbcommon (v2 format)</th>
  </tr>
  </thead>
  <tbody>
  <!-- Additions -->
  <tr>
  <th>Optional keymap components</th>
  <td>❌️ All components are mandatory</td>
  <td colspan="2">
  <details>
  <summary>✅ Full support (since 1.9)</summary>
  Keymap components are no longer mandatory, e.g. a keymap without a
  `xkb_types` section is legal.
  </details>
  </td>
  </tr>
  <tr>
  <th>Strong type check</th>
  <td>❌️ Weak type check</td>
  <td colspan="2">
  <details>
  <summary>⚠️ Stronger type check (WIP)</summary>
  Floating-point numbers cannot be used where an integer is expected.
  </details>
  </td>
  </tr>
  <tr>
  <th>`replace` merge mode in include statements</th>
  <td>❌️ No support</td>
  <td colspan="2">
  <details>
  <summary>✅ Full support (since 1.9)</summary>
  Supported using the prefix `^`, in addition to the standard *merge* `|` and
  *override* `+` modes.
  </details>
  </td>
  </tr>
  <tr>
  <th>Keysym as strings</th>
  <td>❌️ No support</td>
  <td colspan="2">
  <details>
  <summary>✅ Full support (since 1.9)</summary>
  Keysyms can be written as their corresponding string, e.g. `udiaeresis` can be
  written `"ü"`. A string with multiple Unicode code points denotes a list of the
  corresponding keysyms. An empty string denotes the keysym `NoSymbol`.
  </details>
  </td>
  </tr>
  <tr>
  <th>Unicode escape sequence</th>
  <td>❌️ No support</td>
  <td colspan="2">
  <details>
  <summary>✅ Full support (since 1.9)</summary>
  `\u{NNNN}`.
  
  See @ref keymap-string-literal "string literal" for further information.
  </details>
  </td>
  </tr>
  <tr>
  <th>Extended `GroupN` constants</th>
  <td>
  <details>
  <summary>❌️ No support</summary>
  Only `Group1`..`Group8` are supported, although the resulting group must be in
  the range 1..4.
  </details>
  </td>
  <td>
  <details>
  <summary>❌️ No support</summary>
  Only `Group1`..`Group4` are supported.
  
  Use `::XKB_KEYMAP_FORMAT_TEXT_V2` in order to support further groups.
  </details>
  </td>
  <td>
  <details>
  <summary>✅ Full support (since 1.11)</summary>
  The pattern `Group<INDEX>` can be used for any valid group index `<INDEX>`.
  </details>
  </td>
  </tr>
  <tr>
  <th>Extended `LevelN` constants</th>
  <td>
  <details>
  <summary>❌️ No support</summary>
  Only `Level1`..`Level8` are supported.
  </details>
  </td>
  <td colspan="2">
  <details>
  <summary>✅ Full support (since 1.11)</summary>
  Since 1.11, the pattern `Level<INDEX>` can be used for any valid level index
  `<INDEX>`.
  
  Before 1.11, only `Level1`..`Level8` were supported.
  </details>
  </td>
  </tr>
  <tr>
  <th>Extended include</th>
  <td>❌️ No support</td>
  <td colspan="2">
  <details>
  <summary>✅ Full support (since 1.11)</summary>
  Enable *absolute* paths and *`%`-expansion*.
  
  See @ref keymap-include-percent-expansion for further details.
  </details>
  </td>
  </tr>
  <!-- Removals -->
  <tr>
  <th>Include predefined maps</th>
  <td>✅ Full support</td>
  <td colspan="2">
  <details>
  <summary>❌️ No support</summary>
  The modern approach is to use [RMLVO].
  </details>
  </td>
  </tr>
  <tr>
  <th>Exponent syntax for floating-point numbers</th>
  <td>✅ Full support</td>
  <td colspan="2">
  <details>
  <summary>❌️ No support</summary>
  @todo syntax description
  </details>
  </td>
  </tr>
  <tr>
  <th>`alternate` merge mode</th>
  <td>✅ Full support</td>
  <td colspan="2">
  <details>
  <summary>⚠️ Parsing, fallback to default merge mode</summary>
  `alternate` was used in `xkb_keycodes` type sections and meant that if a new
  keycode name conflicts with an old one, consider it as a keycode *alias*.
  </details>
  </td>
  </tr>
  <tr>
  <th>Multiple group definition in symbols section</th>
  <td>✅ Full support</td>
  <td colspan="2">
  <details>
  <summary>⚠️ Supported, except in the [RMLVO] API</summary>
  Since 1.8, only 1 group per symbol section is supported in the [RMLVO] API, to
  avoid unintuitive results.
  
  Multiple groups per symbol section is supported when parsing a [KcCGST] keymap.
  </details>
  </td>
  </tr>
  </tbody>
  </table>
  
  
  ### API
  
  <table>
  <caption>API compatibility table</caption>
  <thead>
  <tr>
  <th>Feature</th>
  <th>X11</th>
  <th>xkbcommon (v1 format)</th>
  <th>xkbcommon (v2 format)</th>
  </tr>
  </thead>
  <tbody>
  <!-- Additions -->
  <tr>
  <th>Full Unicode support</th>
  <td>❌️ Incomplete</td>
  <td colspan="2">
  <details>
  <summary>✅ Full support</summary>
  Full support of simple case mappings for `xkb_keysym_to_lower()` and
  `xkb_keysym_to_upper()`.
  </details>
  </td>
  </tr>
  <!-- TODO -->
  <!-- Removals -->
  <tr>
  <th>[KcCGST] @anchor KcCGST-support</th>
  <td>✅ Full support</td>
  <td colspan="2">
  <details>
  <summary>⚠️ Partial support (since 1.10)</summary>
  - [KcCGST] is considered an implementation detail, use [RMLVO] instead.
  - Use `xkb_component_names::xkb_components_names_from_rules()` for
    debugging purposes.
  </details>
  </td>
  </tr>
  <tr>
  <th>XKM file format</th>
  <td>✅ Full support</td>
  <td colspan="2">
  <details>
  <summary>❌️ No support</summary>
  Obsolete legacy file format tied to X11 ecosystem.
  </details>
  </td>
  </tr>
  <!-- TODO -->
  </tbody>
  </table>
  
  [KcCGST]: @ref KcCGST-intro
  [RMLVO]: @ref RMLVO-intro
  
  
  ## Rules support {#rules-support}
  
  <table>
  <caption>API compatibility table</caption>
  <thead>
  <tr>
  <th>Feature</th>
  <th>X11</th>
  <th>xkbcommon (v1 format)</th>
  <th>xkbcommon (v2 format)</th>
  </tr>
  </thead>
  <tbody>
  <!-- Additions -->
  <tr>
  <th>`! include` statement</th>
  <td>❌️ No support</td>
  <td colspan="2">
  <details>
  <summary>✅ Full support</summary>
  See @ref rules-include-expansion "rules include statement" for further details.
  </details>
  </td>
  </tr>
  <tr>
  <th>`replace` merge mode</th>
  <td>❌️ No support</td>
  <td colspan="2">
  <details>
  <summary>✅ Full support (since 1.9)</summary>
  Support the merge mode *replace* via the prefix `^`, in addition to
  the standard *merge* `|` and *override* `+` modes.
  </details>
  </td>
  </tr>
  <tr>
  <th>Extended layout indices</th>
  <td>❌️ No support</td>
  <td colspan="2">
  <details>
  <summary>✅ Full support (since 1.8)</summary>
  - *single*: matches a single layout; `layout[single]` is the same as without
  explicit index: `layout`.
  - *first*: matches the first layout/variant, no matter how many layouts are in
  the RMLVO configuration. Acts as both `layout` and `layout[1]`.
  - *later*: matches all but the first layout. This is an index range. Acts as
  `layout[2]` .. `layout[MAX_LAYOUT]`, where `MAX_LAYOUT` is currently 4.
  - *any*: matches layout at any position. This is an index range.
  
  - the `:all` qualifier: it applies the qualified item to all layouts.
  
  See @ref rules-extended-layout-indices "extended layout indices" for further
  details.
  </details>
  </td>
  </tr>
  <tr>
  <th>`:all` qualifier</th>
  <td>❌️ No support</td>
  <td colspan="2">
  <details>
  <summary>✅ Full support (since 1.8)</summary>
  the `:all` qualifier: it applies the qualified item to all layouts.
  
  See @ref rules-all-qualifier ":all qualifier" for further
  details.
  </details>
  </td>
  </tr>
  <tr>
  <th>Extended wild cards</th>
  <td>❌️ No support</td>
  <td colspan="2">
  <details>
  <summary>✅ Full support (since 1.9)</summary>
  - `<none>` matches *empty* value;
  - `<some>` matches *non-empty* value in *every* context.
  - `<any>` matches *optionally empty* value in *every* context, contrary to the
    legacy `*` wild card which does not match empty values for layout and variant.
  
  See @ref rules-wildcard-def "rules wildcards" for further information.
  </details>
  </td>
  </tr>
  <!-- Removals -->
  <!-- TODO -->
  </tbody>
  </table>
  
  
  <!-- TODO: tools. Move some of the FAQ entries here? -->
  
  
  ## Keyboard layout registry {#registry-support}
  
  
  <table>
  <caption>Keyboard layout registry support</caption>
  <thead>
  <tr>
  <th>Feature</th>
  <th>X11</th>
  <th>xkbcommon</th>
  </tr>
  </thead>
  <tbody>
  <!-- Additions -->
  <tr>
  <th>XML format</th>
  <td>❌️ No support</td>
  <td>
  <details>
  <summary>✅ Full support</summary>
  @todo rationale
  </details>
  </td>
  </tr>
  <!-- TODO -->
  <!-- Removals -->
  <!-- TODO -->
  </tbody>
  </table>
  
  
  ## Compose support {#compose-support}
  
  Relative to the standard implementation in libX11 (described in the
  Compose(5) man-page):
  
  <table>
  <caption>Compose support</caption>
  <thead>
  <tr>
  <th>Feature</th>
  <th>X11 (`libX11`)</th>
  <th>xkbcommon</th>
  </tr>
  </thead>
  <tbody>
  <!-- Additions -->
  <!-- TODO -->
  <!-- Removals -->
  <tr>
  <th>`[!] MODIFIER` syntax</th>
  <td>✅ Full support</td>
  <td>
  <details>
  <summary>⚠️ Parsing only</summary>
  Syntax: `[([!] ([~] MODIFIER)...) | None] <keysym>`
  
  If the modifier list is preceded by `!` it must match exactly. MODIFIER may be
  one of `Ctrl`, `Lock`, `Caps`, `Shift`, `Alt` or `Meta`. Each modifier may be
  preceded by a `~` character to indicate that the modifier must not be present.
  If `None` is specified, no modifier may be present.
  
  @todo removal rationale
  </details>
  </td>
  </tr>
  <tr>
  <th>Modifier keysyms in sequences</th>
  <td>✅ Full support</td>
  <td>
  <details>
  <summary>⚠️ Parsed, but key events are ignored</summary>
  Modifiers should not be used in Compose sequences. Use keymap’s features or
  a keysym with more appropriate semantics.
  </details>
  </td>
  </tr>
  <tr>
  <th>Interactions with Braille keysyms</th>
  <td>✅ Full support</td>
  <td>
  <details>
  <summary>❌️ No support</summary>
  @todo feature description, removal rationale
  </details>
  </td>
  </tr>
  <!-- TODO -->
  </tbody>
  </table>
  

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