libxkbcommon: The XKB keymap text format, V1

libxkbcommon 1.8.1 Library implementing the XKB specification for parsing keyboard descriptions and handling keyboard state

Loading...
Searching...
No Matches
The XKB keymap text format, V1

This document describes the `XKB_KEYMAP_FORMAT_TEXT_V1` keymap format, as implemented by libxkbcommon.

See also
  For an overview of the role of this format, please see “XKB the keyboard keymap configuration”.
  For examples of keymaps in this format, please see “User-configuration”. For further examples see xkeyboard-config, the standard database of keyboard configuration data.

Note
  Due to the complexity of the format, this document is still is construction. Some additional resources are:
  - Ivan Pascal’s XKB documentation
  - An Unreliable Guide to XKB Configuration
  - The X Keyboard Extension: Protocol Specification
  - How to enhance XKB configuration
  - ArchWiki XKB page

# Terminology

Keycode

  Code that identifies a physical key on a keyboard.

  - Raw keycodes are the numeric identifiers used as input in XKB. They are the result of the low-level processing of the data that keyboards send to a computer. For instance `36` may represent the return key.
  - XKB keycodes are symbolic names assigned to raw keycodes in order to facilitate their mapping to symbols. For instance the keycode for the return key is the abbreviation `RTRN`.

  See xkb_keycodes for further details.

Symbols

  A keysym (short for “key symbol”) is a numeric encoding of a symbol on the cap of a key.

  They have a canonical name for convenience. It can be:

  - A character: e.g. `a` and `A` for Latin scripts, `alpha` “α” and `ALPHA` “Α” for Greek, etc.

  - A dead key: e.g. `dead_grave` and `dead_diaeresis`, corresponding respectively to the grave accent and the diaeresis diacritics.

    A dead key is a special kind of key that does not generate a character by itself, but modifies the character generated by the key struck(s) immediately after.

  - A modifier⁠: e.g. `Shift_L`, `Control_R`, `Caps_Lock`. See hereinafter.
  - A system action: e.g. the arrow `Left`, `Pause`, `Escape`, `F1`.

  The complete list of keysyms is defined in `xkbcommon/xkbcommon-keysyms.h`.

  See xkb_symbols for further details on binding keysyms to keycodes.

Modifier

  A modifier key is a key that modifies the effect of other keys: e.g. Shift, Control, Caps Lock, etc.

  The state of a modifier key (active/inactive) is encoded as a modifier index (or modifier bit or simply modifier) and has an associated unique name.

  For historical reasons, modifiers are divided in two categories:

  Real modifiers

    They are the 8 predefined (AKA core, X11) modifiers (see usual modifiers hereinafter).

    Real modifiers ensure backward compatibility: indeed they are the actual bits used to compute the levels and are communicated via the API of xkbcommon.

    Some are generic modifiers (`Mod[1-5]`) that do not have a conventional interpretation and are the motivation of the introduction of virtual modifiers.

  Virtual modifiers
    They are the modifiers that are not predefined.

  Each modifier defines a mapping to one or multiple real modifier. Real modifiers map to themselves.

  The following table lists the usual modifiers present in the standard keyboard configuration. Note that this is provided for information only, as it may change depending on the user configuration.

  Modifier | Type | Usual mapping | Comment
  --- | --- | --- | ---
  `Shift` | Real | `Shift` | The usual Shift
  `Lock` | Real | `Lock` | The usual Caps Lock
  `Control` | Real | `Control` | The usual Control
  `Mod1` | Real | `Mod1` | Not conventional
  `Mod2` | Real | `Mod2` | Not conventional
  `Mod3` | Real | `Mod3` | Not conventional
  `Mod4` | Real | `Mod4` | Not conventional
  `Mod5` | Real | `Mod5` | Not conventional
  `Alt` | Virtual | `Mod1` | The usual Alt
  `Meta` | Virtual | `Mod1` or `Mod4` | The legacy Meta key
  `NumLock` | Virtual | `Mod2` | The usual NumLock
  `Super` | Virtual | `Mod4` | The usual Super/GUI
  `LevelThree` | Virtual | `Mod3` | ISO level 3, aka AltGr
  `LevelFive` | Virtual | `Mod5` | ISO level 5

  A modifier key can report its state in one of the following 3 ways:

  Depressed
    Active while depressed; e.g. the usual Shift.
  Latched
    Activated when pressed and deactivated after the next non-modifier key press.
  Locked
    Activated when pressed and deactivated when pressed again; e.g. the usual Caps Lock.

  See modifiers bindings for further details.

Shift Level

  A key may produce different results depending of the active modifiers: e.g. for a Latin script, pressing the key A produces “a” and holding Shift while pressing A produces “A”.

  This various results are organized in an ordered list; the index of each entry is called a shift level or simply level. By convention the lowest level is the result when no modifier is active. Example for the key `A` on a latin script keyboard:

  Level | Description | Keysym | Active key modifiers
  --- | --- | --- | ---
  1 | Lower case letters | `a` | None
  2 | Upper case letters. | `A` | `Shift`
  3 | Alternative lower case letters | `ae` | `AltGr`
  4 | Alternative upper case letters | `AE` | `Shift` + `AltGr`

  A key shift level is the logical state of a key corresponding to the current shift level it used.

  Key shift levels are derived from the modifiers states, but not necessarily in the same way for all keys. For example, for Latin script the Caps Lock modifier selects the level 2 for alphabetic keys such as `A` but has no effect on a numeric key.

  There are groups of keys with the same characteristics: letters, punctuation, numeric keypad, etc. The meaning of their levels is identical and thus can be shared: this generalization is called a key type (see hereinafter).

Key type

  A key type defines the levels available for a key and how to derive the active level from the modifiers states. Examples:

  - `ONE_LEVEL`: the key has only one level, i.e. it is not affected by any modifiers. Example: the modifiers themselves.
  - `TWO_LEVEL`: the key has two levels:
    - Level 1: default level, active when the `Shift` modifier is not active.
    - Level 2: level activated with the `Shift` modifier.
  - `FOUR_LEVEL`: see the example in the previous section.

  See xkb_types for further details.

Layout

  A mapping of keycodes to symbols, actions and key types.

  A user who deals with multiple languages may need two or more different layouts: e.g. a layout for Arabic and another one for English. In this context, layouts are called groups in XKB, as defined in the standard ISO/IEC 9995.

  Layouts are ordered and identified by their index. Example:

  - Layout 1: Arabic
  - Layout 2: English

Key Action

  In XKB world, a key action defines the effect a key has on the state of the keyboard or the state of the display server. Examples:

  - Change the state of a modifier.
  - Change the active group.
  - Move the mouse pointer.

  See the section “Key actions” for further details.

Indicator

  A keyboard indicator is a mean to report a specific aspect of the keyboard state.

  Physical indicator
    Typically a labelled LED on the keyboard, e.g. “Caps Lock” and “Num Lock”.
  Logical indicator

    A customizable derived state of the keyboard. Its changes creates events that can be monitored.

    There are two categories:

    - Real indicators are those associated to a physical indicator. For example, the “Caps Lock” logical modifier controls the corresponding physical LED.

      Because indicators are customizable, if one misses a “Num Lock” LED, one could define instead the “Caps Lock” indicator to activate its LED when the “Num Lock” modifier is active.

    - Virtual indicators are not associated to a physical indicator. Their effect is only visible for programs monitoring them.

    Note that the meanings of real and virtual is slightly different than the one used for modifier.

  See: `xkb_keycodes` to define indicators and `xkb_compat` to define their effects.

Keymap

  The complete definition of the mapping of raw keycodes to symbols and actions. It fully defines the behavior of a keyboard.

  Depending of the context, a keymap may refer to:

  - the software object defined and managed by libxkbcommon;
  - the text configuration used to create this software object.

  See Keymap components and xkb_keymap for further details.

Keyboard configuration database
  A database that provides the keymap components. *nix OSs uses the standard database xkeyboard-config. One may extend this database with custom layouts: see “User-configuration” for further details.

# Introduction to the XKB text format

The XKB text format uses a syntax similar to the C programming language. Note that the similarity with C stops here: the XKB text format is only a configuration format and is not intended for programming.

The XKB text format is used to configure a keyboard keymap, which is introduced in “XKB the keyboard keymap configuration”. It has the following two main use cases, illustrated in the diagram hereinafter:

- Server: Load a keymap from the keymap configuration database, then handle input events by updating the keyboard state. The keymap is assembled from an RMLVO configuration and its corresponding KcCGST components files.

  See also
    xkb_keymap::xkb_keymap_new_from_names
    xkeyboard-config for the implementation of the standard Keymap Creation configuration database.
    “User-configuration” to add a custom layout or option.

- Client: Load the active keymap from the server, then handle update events sent by the server. The complete keymap is directly available in a self-contained file.

  See also
    xkb_keymap::xkb_keymap_new_from_string

  XKB text format use cases

## XKB file

There are two kinds of files for the XKB text format:

Keymap file

  A file with the complete description of the keymap object. It is the kind of file that the server sends to the client (see the diagram above). Its top-level structure consists of the xkb_keymap block.

Keymap component file
  A file with the description of a particular KcCGST component. It is the kind of file that the server uses to assemble a keymap file. Its top-level structure consists of a single type of keymap sections. A component file may contain multiple such sections.

## Keymap components

Keymap components are described with keymap sections. They are grouped in keymap component files to form a keyboard configuration database.

Keymap component
  A part of the keymap object. The set of keymap components is referred as KcCGST. They are presented in the table hereinafter.
Keymap section
  A part of the keymap text configuration dedicated to one of the keymap components.
Component folder
  A folder in the keymap configuration database, dedicated to files with partial definitions of the same keymap section.

Keymap components
Component | Section in a keymap | Folder in a keymap configuration database | Description
--- | --- | --- | ---
Key codes | xkb_keycodes | `keycodes` | A translation of the raw key codes from the keyboard into symbolic names.
Compatibility | xkb_compat | `compat` | A specification of what internal actions modifiers and various special-purpose keys produce.
(Geometry) | xkb_geometry | `geometry` | A description of the physical layout of a keyboard. Attention This legacy feature is not supported by xkbcommon.
Key symbols | xkb_symbols | `symbols` | A translation of symbolic key codes into actual key symbols (keysyms).
Key types | xkb_types | `types` | Types describe how a pressed key is affected by active modifiers such as Shift, Control, Alt, etc.

## Comments

Comments are introduced following either `//` or `#` until the end of the line.

## Literals

String literal

  A string is surrounded by double quotes: “`"`”. The following escape sequences are supported:

  Escape sequence | Meaning
  --- | ---
  `\\` | Backslash “`\`”
  `\b` | Backspace
  `\e` | Escape
  `\f` | Form feed
  `\n` | Line feed (newline)
  `\r` | Carriage return
  `\t` | Horizontal tabulation
  `\v` | Vertical tabulation
  `\` + octal number | Corresponding ASCII character: `\0` → NULL, `\42` → `"`

  Note
    The string encoding is unspecified and not validated, but for best results, stick to ASCII.
Number literal

  A number can be written in three forms:

  - decimal integer: `1`, `123`, etc.
  - decimal floating-point number: `1.23`, etc.
  - hexadecimal integer: prefixed with `0x`: `0x123`, `0xff`, `0xAB`, etc.

## Keywords

The following table presents the keywords used in the format. They are case-sensitive.

Keyword | Use
--- | ---
`action` | TODO
`alias` | TODO
`alphanumeric_keys` | TODO
`alternate_group` | TODO
`alternate` | TODO
`augment` | Mode qualifier for include statements
`default` | TODO
`function_keys` | TODO
`group` | TODO
`hidden` | TODO
`include` | Include statement
`indicator` | TODO
`interpret` | Interpret statement
`key` | TODO
`keypad_keys` | TODO
`keys` | TODO
`logo` | TODO
`mod_map` | Alias of `modifier_map`
`modifier_keys` | TODO
`modmap` | Alias of `modifier_map`
`modifier_map` | TODO
`outline` | TODO
`overlay` | TODO
`override` | Mode qualifier for include statements
`partial` | TODO
`replace` | Mode qualifier for include statements
`row` | TODO
`section` | TODO
`shape` | TODO
`solid` | TODO
`text` | TODO
`type` | TODO
`virtual_modifiers` | TODO
`virtual` | TODO
`xkb_compat_map` | Alias of `xkb_compatibility_map`
`xkb_compat` | Alias of `xkb_compatibility_map`
`xkb_compatibility_map` | Declare a compatibility section
`xkb_compatibility` | Alias of `xkb_compatibility_map`
`xkb_geometry` | Declare a geometry section (TODO: legacy)
`xkb_keycodes` | Declare a keycodes section
`xkb_keymap` | Declare a keymap block
`xkb_layout` | TODO
`xkb_semantics` | TODO
`xkb_symbols` | Declare a symbols section
`xkb_types` | Declare a key types section

## Built-in settings

There are many built-in settings; they are explained in the following relevant sections.

These settings are case-insensitive, e.g. the following strings denote the same key word: `SETMODS`, `SetMods`, `setMods` and `setmods`.

## The include mechanism

Todo
  the import mechanism, its qualifiers

# The “xkb_keymap” block

A keymap file consists of a single top-level `xkb_keymap` block, under which are nested the following sections:

`xkb_keycodes`
  A translation of the hardware/evdev scancodes from the keyboard into XKB symbolic keycodes.
`xkb_types`
  A specification of the modifier mask, target level and preserved modifiers various modifiers combination produce.
`xkb_compat`
  A specification of what actions various special-purpose keys produce.
`xkb_symbols`
  A translation of symbolic key codes into actual symbols and actions.

Overview of a keymap file:

xkb_keymap {
xkb_keycodes "XXX" {
// ...
}
xkb_types "XXX" {
// ...
};
xkb_compatibility "XXX" {
// ...
};
xkb_symbols "XXX" {
// ...
};
};
xkb_keymap
Opaque compiled keymap object.

# The “xkb_keycodes” section

This is the simplest section type, and is the first one to be compiled. The purpose of this is mostly to map between the hardware/evdev scancodes and XKB keycodes. Each key is given a name by which it can be referred to later, e.g. in the symbols section.

## Keycode statements

Statements of the form:

    <TLDE> = 49;
    <AE01> = 10;

The above would let 49 and 10 be valid keycodes in the keymap, and assign them the names `TLDE` and `AE01` respectively. The format `<WXYZ>` is always used to refer to a key by name.

The naming convention `<AE01>` is based on the standard ISO/IEC 9995-1. It denotes the position of the key in the keyboard grid. It means: the main alphanumeric section (`A`), row `E` and column `01`.

The following figure illustrates the grid on a staggered standard US QWERTY keyboard. `<AE01>` corresponds to the key `1`.

\ 99 \ 00 \ 01 \ 02 \ 03 \ 04 \ 05…
\ \ \ \ \ \ \
-----------------------------------------
E \ \ ^ \ 1 \ 2 \ 3 \ 4 \ 5…
------------------------------------------
D \ Tab \ Q \ W \ E \ R \ T…
-------------------------------------------
C \Caps \ A \ S \ D \ F \ G…
--------------------------------------------
B \Shift \ Z \ X \ C \ V \ B…
---------------------------------------------
A \Ctrl\GUI \Alt \Space…
----------------------------------------------

In the common case this just maps to the evdev scancodes from `/usr/include/linux/input.h`, e.g. the following definitions:

    #define KEY_GRAVE            41
    #define KEY_1                2

correspond to the ones above. Similar definitions appear in the xf86-input-keyboard driver. Note that in all current keymaps there’s a constant offset of 8 (for historical reasons).

Note that contrary to xkbcommon, the X11 protocol supports keycodes only up to `255`. Therefore, when interfacing with X11, keymaps and applications using keycodes beyond `255` should expect warnings.

If there’s a conflict, like the same name given to different keycodes, or same keycode given different names, it is resolved according to the merge mode which applies to the definitions.

## Alias statements

Statements of the form:

    alias <MENU> = <COMP>;

Allows to refer to a previously defined key (here `<COMP>`) by another name (here `<MENU>`). Conflicts are handled similarly to keycode statements.

## LED name statements

Statements of the form:

    indicator 1 = "Caps Lock";
    indicator 2 = "Num Lock";
    indicator 3 = "Scroll Lock";

Assigns a name to the keyboard LED (AKA indicator) with the given index. The LED may be referred by this name later in the compat section and by the user.

# The “xkb_types” section

This section is the second to be processed, after `xkb_keycodes`. However, it is completely independent and could have been the first to be processed (it does not refer to specific keys as specified in the `xkb_keycodes` section).

This section defines key types, which, given a key and a keyboard state (i.e. modifier state and group), determine the shift level to be used in translating the key to keysyms. These types are assigned to each group in each key, in the `xkb_symbols` section.

Key types are called this way because, in a way, they really describe the “type” of the key (or more correctly, a specific group of the key). For example, an ordinary keymap will provide a type called `KEYPAD`, which consists of two levels, with the second level being chosen according to the state of the Num Lock (or Shift) modifiers. Another example is a type called `ONE_LEVEL`, which is usually assigned to keys such as Escape; these have just one level and are not affected by the modifier state. Yet more common examples are `TWO_LEVEL` (with Shift choosing the second level), `ALPHABETIC` (where Caps Lock may also choose the second level), etc.

## How key types work

Key types define a mapping between the modifiers and shift levels. Key types have four parameters:

Shift level names
  Declare shift levels. Mainly for documentation.
Modifiers filter
  Declare what modifiers should be taken into account in the mapping.
Modifiers mapping
  Lookup table to translate modifiers combinations into shift levels.
Modifiers preservation
  Tweak the computation of consumed modifiers.

Key types are used to compute:

- the shift level: see xkb_state::xkb_state_key_get_level().
- the consumed modifiers: see xkb_state::xkb_state_key_get_consumed_mods() and xkb_state::xkb_state_key_get_consumed_mods2().

The following diagram presents an overview of theses computations:

Use of key types to compute shift level and consumed modifiers

## Type definitions

Statements of the form:

    type "FOUR_LEVEL" { ... }

The above would create a new type named `FOUR_LEVEL`. The body of the definition may include statements of the following forms:

### “level_name” statements

    level_name[Level1] = "Base";

Mandatory for each level in the type.

Gives each level in this type a descriptive name. It isn’t used for anything.

Note: A level may be specified as Level[1-8] or just a number (can be more than 8).

### “modifiers” statement

    modifiers = Shift+Lock+LevelThree;

Mandatory, should be specified only once.

A mask of real and virtual modifiers. These are the only modifiers being considered when matching the modifier state against the type. The other modifiers, whether active or not, are masked out in the calculation.

### “map” entry statements

    map[Shift+LevelThree] = Level4;

Should have at least as many mappings as there are levels in the type.

If the active modifiers, masked with the type’s modifiers (as stated above), match (i.e. equal) the modifiers inside the `map[]` statement, then the level in the right hand side is chosen. For example, in the above, if in the current keyboard state the `Shift` and `LevelThree` modifiers are active, while the `Lock` modifier is not, then the keysym(s) in the 4th level of the group will be returned to the user.

### “preserve” statements

    map[Shift+Lock+LevelThree] = Level5;
    preserve[Shift+Lock+LevelThree] = Lock;

When a key type is used for keysym translation, its modifiers are said to be consumed in this translation. For example, in a simple US keymap, the “G” key is assigned an ordinary `ALPHABETIC` key type, whose modifiers are `Shift` and `Lock`; then for the “G” key, these two modifiers are consumed by the translation. This information is relevant for applications which further process the modifiers, since by then the consumed modifiers have already “done their part” and should be masked out.

However, sometimes even if a modifier had already affected the key translation through the type, it should not be reported as consumed, for various reasons. In this case, a `preserve[]` statement can be used to augment the map entry. The modifiers inside the square brackets should match one of the `map[]` statements in the type (if there is no matching map entry, one mapping to Level1 is implicitly added). The right hand side should consists of modifiers from the type’s modifiers; these modifiers are then “preserved” and not reported as consumed.

Attention
  Consuming a locked modifier does not unlock it and it can be consumed again in further keysym translations.

Note
  Remember that Keysym Transformations may affect the resulting keysym when some modifiers are not consumed.

Remarks
  `preserve` statements may be used to tweak keyboard shorcuts.
  Example of use of `preserve` to tweak `Control` shortcuts. Note it would require further work in order to support other modifiers.
  xkb_types {
  // ...
  type "TWO_LEVEL_PLUS_CONTROL" {
  modifiers = Shift + Control;
  map[None] = Level1;
  map[Shift] = Level2;
  map[Control] = Level3;
  map[Control+Shift] = Level4;
  // Using preserve will make Control not consumed and allow
  // applications to detect keyboard shortcuts with alternative
  // keysyms in levels 3 and 4 rather than the levels 1 and 2.
  preserve[Control] = Control;
  preserve[Control+Shift] = Control;
  level_name[Level1] = "Base";
  level_name[Level2] = "Shift";
  level_name[Level3] = "Tweaked Control";
  level_name[Level4] = "Tweaked Control + Shift";
  };
  };
  xkb_symbols {
  // ...
  // The following key would produce Greek keysym on Base and Shift levels,
  // but will produce the corresponding ASCII Latin keysyms when using Control.
  key <AC01> {
  type[Group1]="TWO_LEVEL_PLUS_CONTROL",
  [Greek_alpha, Greek_ALPHA, a, A]
  };
  };

## Key types examples

### Definitions examples

Note
  The convention is that `Lock` affect only “alphabetic” types. For such types, `Lock` “cancels” `Shift` by default, i.e. `Shift+Lock` has the same result as neither modifier. “semi-alphabetic” types have an asymmetry: their first two levels are alphabetic while the next are not.

#### Two levels

The following examples compare two basic types with two levels: `TWO_LEVEL` and `ALPHABETIC`. They differ on their handling of the `Lock` modifier. See the next section for an illustration with concrete layouts.

`TWO_LEVEL`

Definition code (source)

type "TWO_LEVEL" {
// Only care about Shift; Lock will be filter out
modifiers = Shift;
// Define mapping
map[None] = Level1; // No modifier -> level 1
map[Shift] = Level2; // Exactly Shift -> level 2
// (no map entry with Lock)
// Define level names
level_name[Level1] = "Base";
level_name[Level2] = "Shift";
};

Mapping test

Active modifiers | Filtered modifiers | Match? | Shift level
--- | --- | --- | ---
(none) | (none) | Yes | 1
`Shift` | `Shift` | Yes | 2
`Lock` | (none) | Yes | 1
`Shift + Lock` | `Shift` | Yes | 2

`ALPHABETIC`

Definition code (source)

type "ALPHABETIC" {
// Only care about Shift and Lock
modifiers = Shift + Lock;
// Define mapping
map[None] = Level1; // No modifier -> level 1
map[Shift] = Level2; // Exactly Shift -> level 2
map[Lock] = Level2; // Exactly Lock -> level 2
// Define level names
level_name[Level1] = "Base";
level_name[Level2] = "Caps";
};

Mapping test

Active modifiers | Filtered modifiers | Match? | Shift level
--- | --- | --- | ---
(none) | (none) | Yes | 1
`Shift` | `Shift` | Yes | 2
`Lock` | `Lock` | Yes | 2
`Shift + Lock` | `Shift + Lock` | No | 1

#### Four levels

The following examples compare basic types with four levels: `FOUR_LEVEL`, `FOUR_LEVEL_SEMIALPHABETIC` and `FOUR_LEVEL_ALPHABETIC`. They differ on their handling of the `Lock` modifier. See the next section for an illustration with concrete layouts.

`FOUR_LEVEL`

Definition code (source)

type "FOUR_LEVEL" {
modifiers = Shift + LevelThree;
map[None] = Level1;
map[Shift] = Level2;
// (no map entry with Lock)
// (no map entry with Lock)
map[LevelThree] = Level3;
map[Shift+LevelThree] = Level4;
// (no map entry with Lock)
// (no map entry with Lock)
// (no preserve entry with Lock)
// (no preserve entry with Lock)
level_name[Level1] = "Base";
level_name[Level2] = "Shift";
level_name[Level3] = "AltGr";
level_name[Level4] = "Shift AltGr";
};

Mapping test

Active modifiers | Filtered modifiers | Match? | Shift level
--- | --- | --- | ---
(none) | (none) | Yes | 1
`Shift` | `Shift` | Yes | 2
`Lock` | (none) | Yes | 1
`Shift+Lock` | `Shift` | Yes | 2
`LevelThree` | `LevelThree` | Yes | 3
`LevelThree+Shift` | `LevelThree+Shift` | Yes | 4
`LevelThree+Lock` | `LevelThree` | Yes | 3
`LevelThree+Shift+Lock` | `LevelThree+Shift` | Yes | 4

`FOUR_LEVEL_SEMIALPHABETIC`

Definition code (source)

type "FOUR_LEVEL_SEMIALPHABETIC" {
modifiers = Shift + Lock + LevelThree;
map[None] = Level1;
map[Shift] = Level2;
map[Lock] = Level2;
map[Shift+Lock] = Level1;
map[LevelThree] = Level3;
map[Shift+LevelThree] = Level4;
map[Lock+LevelThree] = Level3;
map[Shift+Lock+LevelThree] = Level4;
preserve[Lock+LevelThree] = Lock;
preserve[Shift+Lock+LevelThree] = Lock;
level_name[Level1] = "Base";
level_name[Level2] = "Shift";
level_name[Level3] = "AltGr";
level_name[Level4] = "Shift AltGr";
};

Mapping test

Active modifiers | Filtered modifiers | Match? | Shift level
--- | --- | --- | ---
(none) | (none) | Yes | 1
`Shift` | `Shift` | Yes | 2
`Lock` | `Lock` | Yes | 2
`Shift+Lock` | `Shift+Lock` | Yes | 1
`LevelThree` | `LevelThree` | Yes | 3
`LevelThree+Shift` | `LevelThree+Shift` | Yes | 4
`LevelThree+Lock` | `LevelThree+Lock` | Yes | 3
`LevelThree+Shift+Lock` | `LevelThree+Shift+Lock` | Yes | 4

`FOUR_LEVEL_ALPHABETIC`

Definition code (source)

type "FOUR_LEVEL_ALPHABETIC" {
modifiers = Shift + Lock + LevelThree;
map[None] = Level1;
map[Shift] = Level2;
map[Lock] = Level2;
map[Shift+Lock] = Level1;
map[LevelThree] = Level3;
map[Shift+LevelThree] = Level4;
map[Lock+LevelThree] = Level4;
map[Shift+Lock+LevelThree] = Level3;
// (no preserve entry with Lock)
// (no preserve entry with Lock)
level_name[Level1] = "Base";
level_name[Level2] = "Shift";
level_name[Level3] = "AltGr";
level_name[Level4] = "Shift AltGr";
};

Mapping test

Active modifiers | Filtered modifiers | Match? | Shift level
--- | --- | --- | ---
(none) | (none) | Yes | 1
`Shift` | `Shift` | Yes | 2
`Lock` | `Lock` | Yes | 2
`Shift+Lock` | `Shift+Lock` | Yes | 1
`LevelThree` | `LevelThree` | Yes | 3
`LevelThree+Shift` | `LevelThree+Shift` | Yes | 4
`LevelThree+Lock` | `LevelThree+Lock` | Yes | 4
`LevelThree+Shift+Lock` | `LevelThree+Shift+Lock` | Yes | 3

### Examples with standard keyboard layouts

See the detailed table of mappings

The following table compares the mappings of various key types for the modifiers `Shift`, `Lock` and `LevelThree`, using the standard layouts `us` (US English) and `es` (Spanish).

Key | Layout | Key type | Active modifiers | Level | Keysym | Comment
--- | --- | --- | --- | --- | --- | ---
`AE01` | `us` | `TWO_LEVEL` | (none) | 1 | `1` |
`Shift` | 2 | `exclam` |
`Lock` | 1 | `1` | `Lock` filtered out
`Shift` + `Lock` | 2 | `exclam` | `Lock` filtered out
`LevelThree` | 1 | `1` | `LevelThree` filtered out
`LevelThree` + `Shift` | 2 | `exclam` | `LevelThree` filtered out
`LevelThree` + `Lock` | 1 | `1` | Modifiers `LevelThree` and `Lock` filtered out
`LevelThree` + `Shift` + `Lock` | 2 | `exclam` | Modifiers `LevelThree` and `Lock` filtered out
`es` | `FOUR_LEVEL` | (none) | 1 | `1` |
`Shift` | 2 | `exclam` |
`Lock` | 1 | `1` | `Lock` filtered out
`Shift` + `Lock` | 2 | `exclam` | `Lock` filtered out
`LevelThree` | 3 | `bar` |
`LevelThree` + `Shift` | 4 | `exclamdown` |
`LevelThree` + `Lock` | 3 | `bar` | `Lock` filtered out
`LevelThree` + `Shift` + `Lock` | 4 | `exclamdown` | `Lock` filtered out
`AD01` | `us` | `ALPHABETIC` | (none) | 1 | `q` |
`Shift` | 2 | `Q` |
`Lock` | 2 | `Q` |
`Shift` + `Lock` | 1 | `q` | `Lock` cancelled by `Shift`
`LevelThree` | 1 | `q` | `LevelThree` filtered out
`LevelThree` + `Shift` | 1 | `q` | `LevelThree` filtered out
`LevelThree` + `Lock` | 2 | `Q` | `LevelThree` filtered out
`LevelThree` + `Shift` + `Lock` | 1 | `q` | `LevelThree` filtered out, `Lock` cancelled by `Shift`
`es` | `FOUR_LEVEL_SEMIALPHABETIC` | (none) | 1 | `q` |
`Shift` | 2 | `Q` |
`Lock` | 2 | `Q` |
`Shift` + `Lock` | 1 | `q` | `Lock` cancelled by `Shift`
`LevelThree` | 3 | `at` |
`LevelThree` + `Shift` | 4 | `Greek_OMEGA` |
`LevelThree` + `Lock` | 3 | `at` | `Lock` does not affect `LevelThree` combos
`LevelThree` + `Shift` + `Lock` | 4 | `Greek_OMEGA` | `Lock` does not affect `LevelThree` combos
`AD05` | `us` | `ALPHABETIC` | (none) | 1 | `t` |
`Shift` | 2 | `T` |
`Lock` | 2 | `T` |
`Shift` + `Lock` | 1 | `t` | `Lock` cancelled by `Shift`
`LevelThree` | 1 | `t` | `LevelThree` filtered out
`LevelThree` + `Shift` | 1 | `t` | `LevelThree` filtered out
`LevelThree` + `Lock` | 2 | `T` | `LevelThree` filtered out
`LevelThree` + `Shift` + `Lock` | 1 | `t` | `LevelThree` filtered out, `Lock` cancelled by `Shift`
`es` | `FOUR_LEVEL_ALPHABETIC` | (none) | 1 | `t` |
`Shift` | 2 | `T` |
`Lock` | 2 | `T` |
`Shift` + `Lock` | 1 | `t` | `Lock` cancelled by `Shift`
`LevelThree` | 3 | `tslash` |
`LevelThree` + `Shift` | 4 | `Tslash` |
`LevelThree` + `Lock` | 4 | `Tslash` |
`LevelThree` + `Shift` + `Lock` | 3 | `tslash` | `Lock` cancelled by `Shift`

# The “xkb_compat” section

This section is the third to be processed, after `xkb_keycodes` and `xkb_types`.

## Interpret statements

Statements of the form:

    interpret Num_Lock+Any { ... }
    interpret Shift_Lock+AnyOf(Shift+Lock) { ... }

The `xkb_symbols` section (see below) allows the keymap author to perform, among other things, the following things for each key:

- Bind an action, like `SetMods` or `LockGroup`, to the key. Actions, like symbols, are specified for each level of each group in the key separately.
- Add a virtual modifier to the key’s virtual modifier mapping (`vmodmap`).
- Specify whether the key should repeat or not.

However, doing this for each key (or level) is tedious and inflexible. Interpret’s are a mechanism to apply these settings to a bunch of keys/levels at once.

Each interpret specifies a condition by which it attaches to certain levels. The condition consists of two parts:

- A keysym. If the level has a different (or more than one) keysym, the match fails. Leaving out the keysym is equivalent to using the special value `Any` or the `NoSymbol` keysym, which always matches successfully.

- A modifier predicate. The predicate consists of:

  - A mask of real modifiers: a `+`-separated list of modifiers or the special value `all`, which denotes all the modifiers.

    The modifiers are matched against the key’s modifier map (`modmap`).

  - A matching operation, that is one of the following:
    - `AnyOfOrNone` – The modmap must either be empty or include at least one of the specified modifiers.
    - `AnyOf` – The modmap must include at least one of the specified modifiers.
    - `Any` – Alias for `AnyOf(all)`.
    - `NoneOf` – The modmap must not include any of the specified modifiers.
    - `AllOf` – The modmap must include all of the specified modifiers (but may include others as well).
    - `Exactly` – The modmap must be exactly the same as the specified modifiers.

  Leaving out the predicate is equivalent to using `AnyOfOrNone(all)`. Leaving out just the matching condition is equivalent to using `Exactly`.

An interpret may also include `useModMapMods = level1;` – see below.

If a level fulfils the conditions of several interprets, only the most specific one is used:

- A specific keysym will always match before a generic `NoSymbol` condition.
- If the keysyms are the same, the interpret with the more specific matching operation is used. The above list is sorted from least to most specific.
- If both the keysyms and the matching operations are the same (but the modifiers are different), the first interpret is used.

As described above, once an interpret “attaches” to a level, it can bind an action to that level, add one virtual modifier to the key’s vmodmap, or set the key’s repeat setting. You should note the following:

- The key repeat is a property of the entire key; it is not level-specific. In order to avoid confusion, it is only inspected for the first level of the first group; the interpret’s repeat setting is ignored when applied to other levels.
- If one of the above fields was set directly for a key in `xkb_symbols`, the explicit setting takes precedence over the interpret.

The body of the statement may include statements of the following forms (all of which are optional):

### “useModMapMods” statement

    useModMapMods = level1;

When set to `level1`, the interpret will only match keysyms which are on the first level of the first group of the keys. This can be useful in conjunction with e.g. a `virtualModifier` statement, because `virtualModifier` is an attribute of the key rather than a specific level.

Note: the other possible value is `any` and is the default value.

### “action” statement

    action = LockMods(modifiers=NumLock);

Bind this action to the matching levels. See key actions for the list of available key actions.

### “virtualModifier” statement

    virtualModifier = NumLock;

Add this virtual modifier to the key’s `vmodmap`. The given virtual modifier must be declared at the top level of the file with a `virtual_modifiers` statement, e.g.:

    virtual_modifiers NumLock;

### “repeat” statement

    repeat = True;

Set whether the key should repeat or not. Must be a boolean value.

## LED map statements

Statements of the form:

    indicator "Shift Lock" { ... }

This statement specifies the behavior and binding of the LED (AKA indicator) with the given name (“Shift Lock” above). The name should have been declared previously in the `xkb_keycodes` section (see LED name statement), and given an index there. If it wasn’t, it is created with the next free index.

The body of the statement describes the conditions of the keyboard state which will cause the LED to be lit. It may include the following statements:

### “modifiers” statement

    modifiers = ScrollLock;

If the given modifiers are in the required state (see below), the LED is lit.

### “whichModState” statement

    whichModState = Latched+Locked;

Can be any combination of:

- `base`, `latched`, `locked`, `effective`
- `any` (i.e. all of the above)
- `none` (i.e. none of the above)
- `compat` (legacy value, treated as effective)

This will cause the respective portion of the modifier state (see `struct xkb_state`) to be matched against the modifiers given in the `modifiers` statement.

Here’s a simple example:

    indicator "Num Lock" {
        modifiers = NumLock;
        whichModState = Locked;
    };

Whenever the NumLock modifier is locked, the Num Lock LED will light up.

### “groups” statement

    groups = All - group1;

If the given groups are in the required state (see below), the LED is lit.

### “whichGroupState” statement

    whichGroupState = Effective;

Can be any combination of:

- `base`, `latched`, `locked`, `effective`
- `any` (i.e. all of the above)
- `none` (i.e. none of the above)

This will cause the respective portion of the group state (see `struct xkb_state`) to be matched against the groups given in the `groups` statement.

Note: the above conditions are disjunctive, i.e. if any of them are satisfied the LED is lit.

## Default values

Todo
  e.g. `setMods.clearLocks= True;`

# The “xkb_symbols” section

This section is the fourth to be processed, after `xkb_keycodes`, `xkb_types` and `xkb_compat`.

Statements of the form:

    xkb_symbols "basic" {
        ...
    }

Declare a symbols map named `basic`. Statements inside the curly braces only affect the symbols map.

A map can have various flags applied to it above the statement, separated by whitespace:

    partial alphanumeric_keys
    xkb_symbols "basic" {
        ...
    }

The possible flags are:

- `partial` - Indicates that the map doesn’t cover a complete keyboard.
- `default` - Marks the symbol map as the default map in the file when no explicit map is specified. If no map is marked as a default, the first map in the file is the default.
- `hidden` - Variant that can only be used internally
- `alphanumeric_keys` - Indicates that the map contains alphanumeric keys
- `modifier_keys` - Indicates that the map contains modifier keys
- `keypad_keys` - Indicates that the map contains keypad keys
- `function_keys` - Indicates that the map contains function keys
- `alternate_group` - Indicates that the map contains keys for an alternate group

If no `*_keys` flags are supplied, then the map is assumed to cover a complete keyboard.

At present, except for `default`, none of the flags affect key processing in libxkbcommon, and only serve as metadata.

## Name statements

Statements of the form:

    name[Group1] = "US/ASCII";
    groupName[1] = "US/ASCII";

Gives the name “US/ASCII” to the first group of symbols. Other groups can be named using a different group index (ex: `Group2`), and with a different name. A group must be named.

`group` and `groupName` mean the same thing, and the `Group` in `Group1` is optional.

## Include statements

Statements of the form:

    include "nokia_vndr/rx-51(nordic_base)"

Will include data from another `xkb_symbols` section, possibly located in another file. Here it would include the `xkb_symbols` section called `nordic_base`, from the file `rx-51` located in the `nokia_vndr` folder, itself located in an XKB include path.

One can use a merge mode prefix to specify the merge mode of the file:

- ‘+’ selects the override merge mode.

- ‘|’ selects the augment merge mode.

  Todo
    dedicated section for merge mode

## Key statement

Statements of the form:

    key <AD01> { ... };

defines the key description of the keycode `<AD01>` and is the main type of record of the `xkb_symbols` section. The possible keycodes are defined in the `xkb_keycodes` section.

A key description consists of:

Groups

  Each key may have one or more associated groups. Each group can be configured with the following parameters:

  - Type
  - Symbols
  - Actions
Additional attributes

  These attributes are usually set via the `xkb_compat` section, but may be also set directly:

  - Virtual modifiers
  - Repeat

Warning
  Using multiple groups in symbols files is not recommended, because some tools rely on the assumption that an `xkb_symbols` section only affect a single group. It is fine with a keymap file though.

Note
  In what follows we assume the common use case with a single group, which benefits from a special syntax. See the section Multiple groups for the general syntax.

### Symbols

The main part of the key description is the symbols table. It maps shift levels to keysyms, e.g.:

key <AD01> { [ q, Q ] }; // Level 1 → `q`, Level 2 → `Q`

Symbols are named using the symbolic names from the `xkbcommon/xkbcommon-keysyms.h` file. A group of symbols is enclosed in brackets and separated by commas. Each element of the symbol arrays corresponds to a different shift level. In this example, the symbol (keysym) `XKB_KEY_q` for level 1 and `XKB_KEY_Q` for level 2. These levels are configured by the key type, presented in the next section.

Remarks
  Remember that Keysym Transformations may affect the resulting keysym when some modifiers are not consumed.

As an extension to the XKB legacy format, libxkbcommon supports multiple key symbols and actions per level (the latter since version 1.8.0):

    key <AD01> { [ {a, b}, Q ] };

In this example, the keycode `<AD01>` produces two symbols on level 1 (`XKB_KEY_a` and `XKB_KEY_b`) and one symbol (`XKB_KEY_Q`) on level 2.

When no actions are explicitly given, they are automatically filled thanks to interpretations from the compat section. In the following example,

    key <LCTL> { [ { Control_L, ISO_Group_Shift } ] };

is equivalent to (given standard definitions from `xkeyboard-config`):

    key <LCTL> {
        symbols[1] = [ { Control_L,                  ISO_Group_Shift    } ],
        actions[1] = [ { SetMods(modifiers=Control), SetGroup(group=+1) } ]
    };

When using this example with e.g. two layouts `fr,us` (respectively Azerty and Qwerty layouts), typing `Control + A` in the first layout `fr` will in fact result in `Control + Q`, because the actions are run sequentially: first set the base modifiers to Control, then switch to the second layout while `Control` is pressed.

Remarks
  Given a level, keysyms and actions may have a different count. For instance, the following would achieve the same effect than the former example with only 1 keysym, but it requires to use 2 explicit actions:
  key <LCTL> {
  symbols[1] = [ Control_L ],
  actions[1] = [ { SetMods(modifiers=Control), SetGroup(group=+1) } ]
  };

Note
  There are some limitations with this extension:

  - For now, at most one action of each following categories is allowed per level:

    - modifier actions: `SetMods`, `LatchMods`, `LockMods`;
    - group actions: `SetGroup`, `LatchGroup`, `LockGroup`.

    Some examples of actions combination:

    - `SetMods` + `SetGroup`: ok
    - `SetMods` + `SetMods`: error
    - `SetMods` + `LockMods`: error
    - `SetMods` + `LockGroup`: ok
  - Multiple actions are only supported from version 1.8.0.

  - Since 1.8.0, `NoSymbol` and `NoAction` are dropped in order to normalize levels:

    // Before normalization
    key <> { [{NoSymbol}, {a, NoSymbol}, {NoSymbol,b}, {a, NoSymbol, b}] };
    // After normalization
    key <> { [NoSymbol, a, b, {a, b}] };

Warning
  Keymaps containing multiple key symbols per level are not supported by the various X11-related tools (`setxkbmap`, `xkbcomp`, etc.).

### Type

Each key has a key type set per group. This key type is defined in the `xkb_types` section. Its associated shift levels are used to index the symbols table presented in the previous section.

A key type is set using the following syntax:

key <AD01> {
type[Group1] = "TWO_LEVEL", // Type
[q, Q] // Symbols
};

The name of the key type is enclosed between double quotes.

The key type may be omitted and will default to:

- `key.type` global defaults, if set.
- a standard type using the following heuristic:
  - 1 keysym: `ONE_LEVEL`
  - 2 keysyms:
    - if the two keysyms are letter and the first is lower case and the other upper case, then `ALPHABETIC`;
    - if one of the keysyms is numpad, then `KEYPAD` else `TWO_LEVEL`.
  - 3 or 4 keysyms (a missing 4th keysym is set to `NoSymbol`):
    - if the first two keysyms are letters and the first is lower case and the other upper case:
      - if the last two keysyms are letters and the first is lower case and the other upper case then `FOUR_LEVEL_ALPHABETIC`;
      - else `FOUR_LEVEL_SEMIALPHABETIC`.
    - if one of the first two keysyms is numpad, then `FOUR_LEVEL_KEYPAD`;
    - else `FOUR_LEVEL`.

Commented examples for inferred types:

// 1 to 2 keysyms
key <LFSH> { [Shift_L] }; // Type: ONE_LEVEL
key <AE01> { [1, exclam] }; // Type: TWO_LEVEL
key <AD01> { [q, Q] }; // Type: ALPHABETIC
key <KP1> { [KP_End, KP_1] }; // Type: KEYPAD
// Edge case: this is consider alphabetic, although
// the lower case does not correspond to the upper case.
key <AD01> { [q, N] }; // Type: ALPHABETIC
// 3 to 4 keysyms
key <AE01> { [1, exclam, bar] }; // Type: FOUR_LEVEL
key <AE01> { [1, exclam, bar, exclamdown] }; // Type: FOUR_LEVEL
key <AD01> { [q, Q, at] }; // Type: FOUR_LEVEL_SEMIALPHABETIC
key <AD01> { [q, Q, at, Greek_OMEGA] }; // Type: FOUR_LEVEL_SEMIALPHABETIC
key <AD05> { [t, T, tslash, Tslash] }; // Type: FOUR_LEVEL_ALPHABETIC
// The inferred type is `FOUR_LEVEL`, but using `LevelThree+Lock`
// will produce `Q`, because of the keysyms transformations and
// the corresponding internal capitalization processing.
key <AE01> { [1, exclam, q, Q] }; // Type: FOUR_LEVEL
// Won’t work, because there is no heuristic for more than 4 keysyms
// It will trigger the warnings XKB-183 and XKB-516 and default to ONE_LEVEL,
// ignoring all the keysyms but the first one.
key <AD01> {[q, Q, at, any, masculine, U2642]};
// Will work as expected
key <AD01> {
type[Group1] = "EIGHT_LEVEL_SEMIALPHABETIC",
[q, Q, at, any, masculine, U2642]
};

### Actions

Note
  This is usually not set explicitly but via the interpret mechanism by using the `action` statement in the `xkb_compat` section.

Example: Set the modifier action of the key `<LALT>` manually.

key <LALT> {
symbols[Group1]=[Alt_L],
actions[Group1]=[SetMods(modifiers=modMapMods)]
};

For further details see key actions.

### Multiple groups

Each group represents a list of symbols mapped to a keycode:

    name[Group1]= "US/ASCII";
    name[Group2]= "Russian";
    ...
    key <AD01> { [ q, Q ],
                 [ Cyrillic_shorti, Cyrillic_SHORTI ] };

A long-form syntax can also be used:

    key <AD01> {
        symbols[Group1]= [ q, Q ],
        symbols[Group2]= [ Cyrillic_shorti, Cyrillic_SHORTI ]
    };

Groups can also be omitted, but the brackets must be present. The following statement only defines the Group3 of a mapping:

    key <AD01> { [], [], [ q, Q ] };

Warning
  Using multiple groups in symbols files is not recommended, because some tools rely on the assumption that an `xkb_symbols` section only affect a single group. It is fine with a keymap file though.

### Virtual modifiers

Note
  This is usually not set explicitly but via the interpret mechanism by using the `virtualModifier` statement from the `xkb_compat` section.

Remarks
  When setting a modifier action, it is required to declare the corresponding virtual modifier using a `virtual_modifiers` statement.

Example: Set the virtual modifier of the key `<LALT>` to `Alt`.

// Declare the virtual modifier that will be used
virtual_modifiers Alt;
key <LALT> {
virtualModifiers = Alt,
[ Alt_L ]
};

### Repeat

Note
  This is usually not set explicitly but via the interpret mechanism by using the `repeat` statement in the `xkb_compat` section.

Example: make the `<LALT>` key not repeating.

key <LALT> {
repeat = False,
[ Alt_L ]
};

# Virtual modifier statements

Statements of the form:

    virtual_modifiers LControl;

Can appear in the `xkb_types`, `xkb_compat`, `xkb_symbols` sections.

# Modifiers bindings

## Real and virtual modifiers

Modifiers are a particularly tricky part of XKB. For historical reasons they are divided in two categories: real modifiers and virtual modifiers.

Note that in X11, the maximum of virtual modifiers is 16 (see `XkbNumVirtualMods`).

The following table summarizes the modifiers defined in `xkeyboard-config` (this is subject to change).

Modifier | Type | Compat files | Associated keysyms
--- | --- | --- | ---
`Shift` | Real | `compat/basic` | `Shift_L`, `Shift_R`
″ | ″ | `compat/iso9995` | `Shift_L`, `Shift_R`, `ISO_Level2_Latch`
`Lock` | Real | `compat/basic`, | `Caps_Lock`
″ | ″ | `compat/caps` | ″
`Control` | Real | `compat/basic` | `Control_L`, `Control_R`
`Alt` | Virtual | `compat/misc`, | `Alt_L`, `Alt_R`
″ | ″ | `compat/pc` | ″
`Meta` | Virtual | `compat/misc` | `Meta_L`, `Meta_R`
`Super` | Virtual | `compat/misc` | `Super_L`, `Super_R`
`Hyper` | Virtual | `compat/misc` | `Hyper_L`, `Hyper_R`
`ScrollLock` | Virtual | `compat/misc` | `Scroll_Lock`
`NumLock` | Virtual | `compat/basic`, | `Num_Lock`,
″ | ″ | `compat/level5` | (`ISO_Level5_Lock`)
`LevelThree` | Virtual | `compat/iso9995` | `ISO_Level3_Shift`, `ISO_Level3_Latch`, `ISO_Level3_Lock`
`LevelFive` | Virtual | `compat/level5` | `ISO_Level5_Shift`, `ISO_Level5_Latch`, `ISO_Level5_Lock`
`Kana_Lock` | Virtual | `compat/japan` | `Kana_Lock`
`Square` | Virtual | `compat/olpc` | `KP_Home`
`Cross` | Virtual | `compat/olpc` | `KP_Next`
`Circle` | Virtual | `compat/olpc` | `KP_End`
`Triangle` | Virtual | `compat/olpc` | `KP_Prior`

## Define and use a modifier

We will use the example of the real modifier `Shift` and the virtual modifier `LevelThree` in `xkeyboard-config`.

In order to define and use a modifier, one must:

1. Define its behavior and keysym binding in the `xkb_compat` section:

   // Declare virtual modifiers. Shift being real modifier,
   // we do not need to add it here.
   virtual_modifiers LevelThree;
   // Set defaults. They are overridden if set directly in the xkb_symbols.
   interpret.repeat= False; // only applied on first level
   setMods.clearLocks= True;
   latchMods.clearLocks= True;
   latchMods.latchToLock= True;
   // Default statement for real modifiers: any key bound to a real
   // modifier via modifier_map will set this modifier at all its
   // levels.
   // Here only to illustrate: do not add it!
   interpret Any + Any {
   action= SetMods(modifiers=modMapMods);
   };
   // Shift being real modifier, we do not need a corresponding
   // interpret statement because the previous one suffices.
   // Let’s associate LevelThree to the keysym ISO_Level3_Shift
   // First, match the keys and their levels with the
   // ISO_Level3_Shift keysym and with any real modifier
   // (Any = AnyOf(all)) in its modmap.
   interpret ISO_Level3_Shift+Any {
   // Only match the first level of the first group
   useModMapMods= level1;
   // Add the virtual modifier to the key’s vmodmap
   virtualModifier= LevelThree;
   // Activate the LevelThree modifier (depressed mode)
   action= SetMods(modifiers=LevelThree);
   };
   // Then for keys and their levels with the
   // ISO_Level3_Shift keysym but with either no real modifier
   // in its modmap or a level higher than 1.
   // Indeed:
   // • In case the level is higher than 1 there is no match
   // in the previous statement.
   // • The condition is equivalent to
   // ISO_Level3_Shift+AnyOfOrNone(all), but since
   // the previous statement ISO_Level3_Shift+Any is more
   // specific, it will be matched before this one.
   interpret ISO_Level3_Shift {
   // Activate the LevelThree modifier (depressed mode)
   action= SetMods(modifiers=LevelThree);
   };

2. Define key types that use it in the `xkb_types` section:

   // Declare virtual modifiers. Shift being real modifier,
   // we do not need to add it here.
   virtual_modifiers LevelThree;
   type "FOUR_LEVEL" {
   // Key type modifier mask: all the modifiers used in the key type
   modifiers = Shift + LevelThree;
   map[None] = Level1;
   map[Shift] = Level2;
   map[LevelThree] = Level3;
   map[Shift+LevelThree] = Level4;
   level_name[Level1] = "Base";
   level_name[Level2] = "Shift";
   level_name[Level3] = "AltGr";
   level_name[Level4] = "Shift AltGr";
   };

3. Bind it to a keycode in the `xkb_symbols` section:

   1. Map keysyms used in the `xkb_compat` section hereinabove.
   2. Bind real modifiers to keys using these keysyms with `modifier_map`.

   Note: Only one key binding to real modifier is required. The corresponding keysym must then be on the first level of the first Group.

   Note: One can optionally bind directly a virtual modifier to a key using `virtualmodifiers` instead of doing it in the `xkb_compat` section. But the recommended way is to use the `xkb_compat` section.

   // Shift: defined in pc symbols
   key <LFSH> {[ Shift_L ]};
   key <RTSH> {[ Shift_R ]};
   modifier_map Shift { Shift_L, Shift_R };
   // The previous will resolve to:
   // modifier_map Shift { <LFSH>, <RTSH> };
   // Thus the real modifier Shift is added to the modmap of
   // <LFSH> and <RTSH>.
   // The “Any + Any” interpret statement matches <LFSH> and <RTSH>,
   // therefore these keys set the Shift modifier.
   // LevelThree: defined in pc symbols
   // With the following 2 lines:
   // 1. The modifier keysym is on the first level of the first group.
   // 2. The real modifier Mod5 is bound to <LVL3>,
   // i.e. Mod5 is added to its modmap.
   // 3. It matches the interpret statement “ISO_Level3_Shift+Any”,
   // which adds the LevelThree modifier to the vmodmap of <LVL3>.
   // 4. The mapping of LevelThree to real modifiers is the union
   // of modmaps with corresponding vmodmaps containing
   // LevelThree. In our case there is only one: therefore
   // LevelThree maps to Mod5.
   key <LVL3> {[ ISO_Level3_Shift ]};
   modifier_map Mod5 { <LVL3> };
   // LevelThree: defined in level3 symbols
   // Not bound to a real modifier, so interpret statement
   // “ISO_Level3_Shift” applies.
   key <RALT> {[ISO_Level3_Shift], type[group1]="ONE_LEVEL" };
   // Note: we could have the following line, but it is not necessary
   // because we have the mappings of <LVL3>.
   // modifier_map Mod5 { <RALT> };
   // Warning: if we had the for example the following line, the
   // mapping of LevelThree to real modifiers would be “Mod1+Mod5”.
   // modifier_map Mod1 { <RALT> };
   // Alternative definitions, without using interpret statements
   virtual_modifiers LevelThree;
   key <LVL3> { virtualmodifiers=LevelThree
   , repeats=False
   , symbols[Group1] = [ISO_Level3_Shift]
   , actions[Group1] = [SetMods(modifiers=LevelThree)] };
   modifier_map Mod5 { <LVL3> };
   key <RALT> { repeat=False
   , symbols[Group1] = [ISO_Level3_Shift]
   , actions[Group1] = [SetMods(modifiers=LevelThree)]
   , type[group1]="ONE_LEVEL" };
   // FOUR_LEVEL key type example from latin symbols
   key <AB05> {[b, B, leftdoublequotemark, leftsinglequotemark]};

# Key actions

Todo
  list of all actions and their parameters

The following table provide an overview of the available actions:

Category | Action | Alias | Description
--- | --- | --- | ---
| `NoAction` |  | Do nothing.
Modifier action | `SetMods` |  | Modifies the depressed modifiers
`LatchMods` |  | Modifies the latched modifiers
`LockMods` |  | Modifies the locked modifiers
Group action | `SetGroup` |  | TODO
`LatchGroup` |  | TODO
`LockGroup` |  | TODO
Legacy action | `MovePointer` | `MovePtr` | TODO
`PointerButton` | `PtrBtn` | TODO
`LockPointerButton` | `LockPtrBtn` | TODO
`SetPointerDefault` | `SetPtrDflt` | TODO
`SetControls` |  | TODO
`LockControls` |  | TODO
`TerminateServer` | `Terminate` | TODO
`SwitchScreen` |  | TODO
`Private` |  | TODO

Common syntax:

- Boolean values:
  - `true`, `yes`, `on`
  - `false`, `no`, `off`

## Modifiers actions

Todo
  default values

There are 3 modifiers actions:

`SetMods`

  Modifies the depressed modifiers.

  Parameters:

  - `modifiers` or `mods`: the list of modifiers to modify, separated by `+`, or the special value `modMapMods`. The latter means the parameter value has to be read from the `vmodmap` attribute of the key.
  - `clearLocks`: boolean (see its use hereinafter).
`LatchMods`

  Modifies the latched modifiers

  Parameters:

  - `modifiers` or `mods`: see `SetMods`.
  - `clearLocks`: boolean (see its use hereinafter).
  - `latchToLock`: boolean (see its use hereinafter).
`LockMods`

  Modifies the locked modifiers.

  Parameters:

  - `modifiers` or `mods`: see `SetMods`.
  - `affect`:
    - `lock`: the action only locks the modifier, but cannot unlock it.
    - `unlock`: the action only unlocks modifier, but cannot lock it.
    - `both`: the first key press locks the modifier and the second key press releases the modifier. It is a default mode.
    - `neither`: do not lock nor unlock, i.e. do nothing.

Todo
  highlight that there is reference counting for the modifiers, e.g. to manage multiple physical keys for the same modifier.

These actions perform different tasks on key press and on key release:

Effects of modifiers actions
Action | On key press | On key release
--- | --- | ---
`SetMods` | Adds modifiers to depressed modifiers | Removes modifiers from depressed modifiers, provided that no other key which affects the same modifiers is logically down. If `clearLocks=yes` and no other key were operated simultaneously with this key, then the modifiers will be removed as well from the locked modifiers.
`LatchMods` | Adds modifiers to latched modifiers. | Removes modifiers from latched modifiers. If `clearLocks=yes` and no other key has been pressed since this key press, then the modifiers will be removed as well from the locked modifiers. If `latchToLock=yes` then the modifiers are added to the locked modifiers.
`LockMods` | Adds modifiers to depressed modifiers. Toggle these modifiers in locked modifiers. | Removes modifiers from depressed modifiers. Locked modifiers stay unchanged.

Todo
  Finish

## Group actions

There are 3 group actions:

SetGroup
  TODO
LatchGroup
  TODO
LockGroup
  TODO

Todo
  Describe each action

## Unsupported legacy actions

Attention
  The following legacy actions are kept for compatibility only: they are parsed and validated but have no effect. This allows to use keymaps defined in `xkeyboard-config` for both X11 and Wayland.

### Pointer actions

Action | Alias | Description
--- | --- | ---
`MovePointer` | `MovePtr` |
`PointerButton` | `PtrBtn` |
`LockPtrButton` | `LockPtrBtn` |
`LockPointerButton` | `LockPointerBtn` |
`SetPointerDefault` | `SetPtrDflt` |

Todo
  Describe each action

### Control flags actions

Todo
  `SetControls`, `LockControls`

### Server actions

Todo
  `TerminateServer`, `SwitchScreen`

### Private action

Todo
  `Private`