3 This page describes how to add a custom layout or option so that it will be
4 parsed by libxkbcommon.
6 **The below requires libxkbcommon as keymap compiler and does not work in X**.
10 libxkbcommon searches the following paths for XKB configuration files:
11 - `$XDG_CONFIG_HOME/xkb/`, or `$HOME/.config/xkb/` if the `$XDG_CONFIG_HOME`
12 environment variable is not defined
14 - `$XKB_CONFIG_EXTRA_PATH` if set, otherswise `<sysconfdir>/xkb` (on most
15 distributions this is `/etc/xkb`)
16 - `$XKB_CONFIG_ROOT` if set, otherwise `<datadir>/X11/xkb/` (path defined by the
17 `xkeyboard-config` package, on most distributions this is
20 A keymap created with `xkb_keymap_new_from_names()` will look up those paths in
21 order until the required data is found.
23 **Note: Where libxkbcommon runs in a privileged context, only the system
24 (datadir) path is available.**
26 Each directory should have one or more of the following subdirectories:
28 - `geometry` (libxkbcommon ignores this directory)
36 Due to how XKB is configured, there is no such thing as a "layout" in XKB
37 itself, or, indeed, any of the rules, models, variant, options (RMLVO) decribed
38 in `struct xkb_rule_names`. RMLVO names are merely lookup keys in the
39 rules file provided by xkeyboard-config to map to the correct keycode, compat,
40 geometry (ignored by libxkbcommon), symbols and types (KcCGST). The KcCGST data
41 is the one used by XKB and libxbkcommon to map keys to actual symbols.
43 For example, a common RMLVO configuration is layout "us", variant "dvorak" and
44 option "terminate:ctrl_alt_bksp". Using the default rules file and model
45 this maps into the following KcCGST components:
49 xkb_keycodes { include "evdev+aliases(qwerty)" };
50 xkb_types { include "complete" };
51 xkb_compat { include "complete" };
52 xkb_symbols { include "pc+us(dvorak)+inet(evdev)+terminate(ctrl_alt_bksp)" };
53 xkb_geometry { include "pc(pc105)" };
57 A detailed explanation of how rules files convert RMLVO to KcCGST is out of
58 scope for this document. See [the rules file](md_doc_rules-format.html) page
64 Adding a layout requires that the user adds **symbols** in the correct location.
66 The default rules files (usually `evdev`) have a catch-all to map a layout, say
67 "foo", and a variant, say "bar", into the "bar" section in the file
68 `$xkb_base_dir/symbols/foo`.
69 This is sufficient to define a new keyboard layout. The example below defines
70 the keyboard layout "banana" with an optional variant "orange"
73 $ cat $XDG_CONFIG_HOME/xkb/symbols/banana
74 // Like a US layout but swap the top row so numbers are on Shift
75 default partial alphanumeric_keys
78 name[Group1]= "Banana (US)";
80 key <AE01> { [ exclam, 1] };
81 key <AE02> { [ at, 2] };
82 key <AE03> { [ numbersign, 3] };
83 key <AE04> { [ dollar, 4] };
84 key <AE05> { [ percent, 5] };
85 key <AE06> { [ asciicircum, 6] };
86 key <AE07> { [ ampersand, 7] };
87 key <AE08> { [ asterisk, 8] };
88 key <AE09> { [ parenleft, 9] };
89 key <AE10> { [ parenright, 0] };
90 key <AE11> { [ underscore, minus] };
91 key <AE12> { [ plus, equal] };
94 // Same as banana but map the euro sign to the 5 key
95 partial alphanumeric_keys
96 xkb_symbols "orange" {
97 include "banana(basic)"
98 name[Group1] = "Banana (Eurosign on 5)";
103 The `default` section is loaded when no variant is given. The first example
104 sections uses ``include`` to populate with a symbols list defined elsewhere
105 (here: section `basic` from the file `symbols/us`, aka. the default US keyboard
106 layout) and overrides parts of these
107 symbols. The effect of this section is to swap the numbers and symbols in the
108 top-most row (compared to the US layout) but otherwise use the US layout.
110 The "orange" variant uses the "banana" symbols and includes a different section
111 to define the eurosign. It does not specificially override any symbols.
113 The exact details of how `xkb_symbols` work is out of scope for this document.
117 For technical reasons, options do **not** have a catch-all to map option names
118 to files and sections and must be specifically mapped by the user. This requires
119 a custom rules file. As the `evdev` ruleset is hardcoded in many clients, the
120 custom rules file must usually be named `evdev`.
123 $ cat $XDG_CONFIG_HOME/xkb/rules/evdev
125 custom:foo = +custom(bar)
126 custom:baz = +other(baz)
131 This rules file maps the RMLVO option "custom:foo" to the "bar" section in the
132 `symbols/custom` file and the "custom:baz" option to the "baz" section in the
133 `symbols/other` file. Note how the RMLVO option name may be different to the
134 file or section name.
136 The `include` statement includes the system-provided `evdev` ruleset. This
137 allows users to only override those options they need.
139 The files themselves are similar to the layout examples in the previous section:
142 $ cat $XDG_CONFIG_HOME/xkb/symbols/custom
143 // map the Tilde key to nothing on the first shift level
144 partial alphanumeric_keys
146 key <TLDE> { [ VoidSymbol ] };
149 $ cat $XDG_CONFIG_HOME/xkb/symbols/other
150 // map first key in bottom row (Z in the US layout) to k/K
151 partial alphanumeric_keys
153 key <AB01> { [ k, K ] };
157 With these in place, a user may select any layout/variant together with
158 the "custom:foo" and/or "custom:baz" options.
160 ## Discoverable layouts
162 **The below requires libxkbregistry as XKB lookup tool and does not work where
163 clients parse the XML file directly**.
165 The above sections apply only to the data files and require that the user knows
166 about the existence of the new entries. To make custom entries discoverable by
167 the configuration tools (e.g. the GNOME Control Center), the new entries must
168 also be added to the XML file that is parsed by libxkbregistry. In most cases,
169 this is the `evdev.xml` file in the rules directory. The example below shows the
170 XML file that would add the custom layout and custom options as outlined above
174 $ cat $XDG_CONFIG_HOME/xkb/rules/evdev.xml
175 <?xml version="1.0" encoding="UTF-8"?>
176 <!DOCTYPE xkbConfigRegistry SYSTEM "xkb.dtd">
177 <xkbConfigRegistry version="1.1">
182 <shortDescription>ban</shortDescription>
183 <description>Banana</description>
189 <shortDescription>or</shortDescription>
190 <description>Orange (Banana)</description>
195 <group allowMultipleSelection="true">
198 <description>Custom options</description>
202 <name>custom:foo</name>
203 <description>Map Tilde to nothing</description>
208 <name>custom:baz</name>
209 <description>Map Z to K</description>
217 The default behavior of libxkbregistry ensures that the new layout and options
218 are added to the system-provided layouts and options.
220 For details on the XML format, see DTD in `<datadir>/X11/xkb/rules/xkb.dtd`
221 and the system-provided XML files in `<datadir>/X11/xkb/rulies/xkb.dtd`.