kc3-lang/libxkbcommon/doc/keymap-format-text-v1.md

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The XKB keymap text format, V1 {#keymap-text-format-v1}

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

The standard database of keyboard configuration data is xkeyboard-config.

@note Due to the complexity of the format, this document is still is construction. Some additional resources are:

@note

@tableofcontents{html:2}

[terminology]: @ref terminology [introduction]: @ref introduction [xkb_keymap]: @ref the-xkb_keymap-block [xkb_keycodes]: @ref the-xkb_keycodes-section [xkb_types]: @ref the-xkb_types-section [xkb_compat]: @ref the-xkb_compat-section [xkb_symbols]: @ref the-xkb_symbols-section [virtual modifier statements]:@ref virtual-modifier-statements [modifiers bindings]: @ref modifiers-bindings [actions]: @ref key-actions

Terminology {#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](https://en.wikipedia.org/wiki/Grave_accent) and the [diaeresis](https://en.wikipedia.org/wiki/Diaeresis_%28diacritic%29) diacritics. A [dead key](https://en.wikipedia.org/wiki/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][level] 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 <a name=”usual-modifiers”>usual modifiers</a> 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

[usual modifiers]: @ref usual-modifiers

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

<dl>

<dt><a name="depressed-mod-def">Depressed</a></dt>
<dd>Active while depressed; e.g. the usual Shift.</dd>
<dt><a name="latched-mod-def">Latched</a></dt>
<dd>
  Activated when pressed and deactivated after the next
  non-modifier key press.
</dd>
<dt><a name="locked-mod-def">Locked</a></dt>
<dd>
  Activated when pressed and deactivated when pressed again;
  e.g. the usual Caps Lock.
</dd>

See [modifiers bindings] for further details.

[depressed]: @ref depressed-mod-def [latched]: @ref latched-mod-def [locked]: @ref locked-mod-def

<dt><a name=”level-def”>Shift Level</a></dt> <dd> 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 <a name=”level-index-def”>shift level</a> or simply level. By convention the lowest level is the result when no modifier is active. Example for the key A on 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).

<dt><a name=”key-type-def”>Key type</a></dt> <dd> 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.

<dt><a name=”layout-def”>Layout</a></dt> <dd> 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&nbsp;9995.

Layouts are ordered and identified by their index. Example:

  • Layout 1: Arabic
  • Layout 2: English

<dt><a name=”key-action-def”>Key Action</a></dt> <dd> 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][actions]” for further details.

<dt><a name=”indicator-def”>Indicator</a></dt> <dd> A keyboard indicator is a mean to report a specific aspect of the keyboard state.

<dl>

<dt><em>Physical</em> indicator</dt>
<dd>
Typically a labelled LED on the keyboard, e.g. “Caps Lock” and
“Num Lock”.
</dd>
<dt><em>Logical</em> indicator</dt>
<dd>
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].
</dd>

See: <code>[xkb_keycodes][indicator name]</code> to define indicators and <code>[xkb_compat][indicator effect]</code> to define their effects.

<dt><a name=”keymap-def”>Keymap</a></dt> <dd> The complete definition of the mapping of raw keycodes to symbols and actions. It fully defines the behavior of a keyboard.

See [xkb_keymap] for further details.

[keycode]: @ref keycode-def [keysym]: @ref keysym-def [keysyms]: @ref keysym-def [modifier]: @ref modifier-def [modifiers]: @ref modifier-def [real modifier]: @ref real-modifier-def [real modifiers]: @ref real-modifier-def [virtual modifier]: @ref virtual-modifier-def [virtual modifiers]: @ref virtual-modifier-def [level]: @ref level-def [shift level]: @ref level-def [level index]: @ref level-index-def [key type]: @ref key-type-def [key types]: @ref key-type-def [layout]: @ref layout-def [action]: @ref key-action-def [indicator]: @ref indicator-def [keymap]: @ref keymap-def

Introduction to the XKB text format {#introduction}

The XKB text format uses a syntax similar to the C programming language.

@todo general comment on syntax: section, values, etc.

@todo the import mechanism

@todo recommended ways to feed xkbcommon

Keywords

@todo keywords, other settings such as “SetMods”

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.

The “xkb_keymap” block {#the-xkb_keymap-block}

A <strong>[keymap]</strong> 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" {
    // ...
  };
};

The “xkb_keycodes” section {#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&nbsp;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 {#indicator-name}

[indicator name]: @ref indicator-name

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 {#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.

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”. For example, in a simple US keymap, the “g” “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.

The “xkb_compat” section {#the-xkb_compat-section}

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

Interpret statements {#interpret-statements}

Statements of the form:

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

The <code>[xkb_symbols]</code> 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 <strong>[keysym]</strong>. 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 <strong>[modifier] predicate</strong>. 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][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 {#indicator-effect}

[indicator effect]: @ref indicator-effect

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][indicator 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 {#the-xkb_symbols-section}

@todo complete this 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.

Key statement

Statements of the form:

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

Describes the mapping of a keycode <AD01> to a given group of symbols. The possible keycodes are the keycodes defined in the xkb_keycodes section.

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 modifier level. In this example, the symbol (keysym) XKB_KEY_q for level 1 and XKB_KEY_Q for level 2.

Actions

@todo how to bind key actions

For further details see [key actions][actions].

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 ] };

Additional attributes

@todo virtualmodifiers, repeats

Virtual modifier statements {#virtual-modifier-statements}

@todo rework this section

Statements of the form:

virtual_modifiers LControl;

Can appear in the xkb_types, xkb_compat, xkb_symbols sections.

Modifiers bindings {#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 <code>xkeyboard-config</code> (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 <code>[xkb_compat]</code> 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 <code>[xkb_types]</code> 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 <code>[xkb_symbols]</code> 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 {#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 <span class=”todo”>TODO</span>
^ LatchGroup <span class=”todo”>TODO</span>
^ LockGroup <span class=”todo”>TODO</span>
[Legacy action] MovePointer MovePtr <span class=”todo”>TODO</span>
^ PointerButton PtrBtn <span class=”todo”>TODO</span>
^ LockPointerButton LockPtrBtn <span class=”todo”>TODO</span>
^ SetPointerDefault SetPtrDflt <span class=”todo”>TODO</span>
^ SetControls <span class=”todo”>TODO</span>
^ LockControls <span class=”todo”>TODO</span>
^ TerminateServer Terminate <span class=”todo”>TODO</span>
^ SwitchScreen <span class=”todo”>TODO</span>
^ Private <span class=”todo”>TODO</span>

Common syntax:

  • Boolean values:
    • true, yes, on
    • false, no, off

Modifiers actions {#modifiers-actions}

[modifier action]: @ref 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 {#group-actions}

[group action]: @ref group-actions

There are 3 group actions:

SetGroup
TODO
LatchGroup
TODO
LockGroup
TODO

@todo Describe each action

Unsupported legacy actions {#legacy-actions}

[legacy action]: @ref 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]

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

Source

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