libxkbcommon 1.6.0
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The purpose of the rules file is to map between configuration values that are easy for a user to specify and understand, and the configuration values xkbcomp uses and understands.
xkbcomp uses the xkb_component_names
struct, which maps directly to include statements of the appropriate sections, called for short KcCGST (see the XKBintroduction";
'G' stands for "geometry", which is not supported). These are not
really intuitive or straight-forward for the uninitiated.
Instead, the user passes in a <tt>xkb_rule_names</tt> struct, which consists
of the name of a rules file (in Linux this is usually "evdev"), a
keyboard model (e.g. "pc105"), a set of layouts (which will end up
in different groups, e.g. "us,fr"), variants (used to alter/augment
the respective layout, e.g. "intl,dvorak"), and a set of options
(used to tweak some general behavior of the keyboard, e.g.
"ctrl:nocaps,compose:menu" to make the Caps Lock key act like Ctrl
and the Menu key like Compose). We call these
@ref RMLVO-intro "RMLVO".
@section autotoc_md19 Format of the file
The file consists of rule sets, each consisting of rules (one per
line), which match the MLVO values on the left hand side, and, if
the values match to the values the user passed in, results in the
values on the right hand side being added to the resulting KcCGST.
Since some values are related and repeated often, it is possible
to group them together and refer to them by a group name in the
rules.
Along with matching values by simple string equality, and for
membership in a group defined previously, rules may also contain
"wildcard" values - "*" - which always match. These usually appear
near the end.
@section autotoc_md20 Grammar
(It might be helpful to look at a file like rules/evdev along with
this grammar. Comments, whitespace, etc. are not shown.)
@icode
File ::= { "!" (Include | Group | RuleSet) }
Include ::= "include" <ident>
Group ::= GroupName "=" { GroupElement } "
"
GroupName ::= "$"<ident>
GroupElement ::= <ident>
RuleSet ::= Mapping { Rule }
Mapping ::= { Mlvo } "=" { Kccgst } "
"
Mlvo ::= "model" | "option" | ("layout" | "variant") [ Index ]
Index ::= "[" 1..XKB_NUM_GROUPS "]"
Kccgst ::= "keycodes" | "symbols" | "types" | "compat" | "geometry"
Rule ::= { MlvoValue } "=" { KccgstValue } "
"
MlvoValue ::= "*" | GroupName | <ident>
KccgstValue ::= <ident>
@endicode
Notes:
- Include processes the rules in the file path specified in the ident,
in order. %-expansion is performed, as follows:
@icode
%%:
A literal %.
%H:
The value of the HOME environment variable.
%E:
The extra lookup path for system-wide XKB data (usually /etc/xkb/rules).
%S:
The system-installed rules directory (usually /usr/share/X11/xkb/rules).
@endicode
- The order of values in a Rule must be the same as the Mapping it
follows. The mapping line determines the meaning of the values in
the rules which follow in the RuleSet.
- If a Rule is matched, %-expansion is performed on the KccgstValue,
as follows:
@icode
%m, %l, %v:
The model, layout or variant, if only one was given (e.g.
%l for "us,il" is invalid).
%l[1], %v[1]:
Layout or variant for the specified group Index, if more than
one was given (e.g. %l[1] for "us" is invalid).
%+m, %+l, %+v, %+l[1], %+v[1]
As above, but prefixed with '+'. Similarly, '|', '-', '_' may be
used instead of '+'.
%(m), %(l), %(l[1]), %(v), %(v[1]):
As above, but prefixed by '(' and suffixed by ')'.
@endicode
In case the expansion is invalid, as described above, it is
skipped (the rest of the string is still processed); this includes
the prefix and suffix (that's why you shouldn't use e.g. "(v[1])").