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= Highlighters

== Description

Manipulation of the displayed text is done through highlighters, which can
be added or removed with the following commands:

----------------------------------------------------------------------
add-highlighter <path> <highlighter_name> <highlighter_parameters> ...
----------------------------------------------------------------------

and

------------------------------------------
remove-highlighter <path>/<highlighter_id>
------------------------------------------

*path* is the name of an highlighter group, it is expressed as a */*
separated path starting with a scope. Scopes are *global*, *buffer*,
*window* and *shared*

*highlighter_id* is a name generated by the highlighter specified with
*highlighter_name*, possibly dependent on the parameters. Use command
completion in a prompt on the *remove-highlighter* command to see the
existing highlighters ids.

== Convenient highlighters

*show_matching*::
    highlight matching char of the character under the selections' cursor
    using `MatchingChar` face

*show_whitespaces* [options]::
    display symbols on top of whitespaces to make them more explicit
    using the `Whitespace` face, with the following *options*:

    *-lf* <separator>:::
        a one character long separator that will replace line feeds

    *-spc* <separator>:::
        a one character long separator that will replace spaces

    *-nbsp* <separator>:::
        a one character long separator that will replace non-breakable spaces

    *-tab* <separator>:::
        a one character long separator that will replace tabulations

    *-tabpad* <separator>:::
        a one character long separator that will be appended to tabulations to honor the *tabstop* option

*number_lines* [options]::
    show line numbers using the `LineNumbers`, `LineNumberCursor` and `LineNumbersWrapped` faces,
    with the following *options*: 

    *-relative*:::
        show line numbers relative to the main cursor line

    *-hlcursor*:::
        highlight the cursor line with a separate face

    *-separator* <separator text>:::
        specify a string to separate the line numbers column with
        the rest of the buffer (default is '|')

*wrap* [options]::
    soft wrap buffer text at window width, with the following *options*:

    *-word*:::
        wrap at word boundaries instead of codepoint boundaries.

    *-indent*:::
        preserve line indent when wrapping.

    *-width <max_width>*:::
        wrap text at *max_width* if the window is wider.

    *-marker <marker_text>*:::
        prefix wrapped lines with *marker_text*; if *-indent* was given,
        the marker_text is displayed into the indentation if possible.

== General highlighters

*fill* <face>::
    fill using the given *face*, mostly useful with regions highlighters

*column* <number> <face>::
    highlight column *number* with face *face*

*line* <number> <face>::
    highlight line *number* with face *face*

*regex* <regex> <capture_id>:<face> ...::
    highlight a regex, takes the regex as first parameter, followed by
    any number of face parameters.
    This highlights C++ style comments in cyan, with an eventual 'TODO:'
    in yellow on red background:

-------------------------------------------------------------------
add-highlighter window regex //\h*(TODO:)[^\n]* 0:cyan 1:yellow,red
-------------------------------------------------------------------

*dynregex* <expression> <capture_id>:<face> ...::
    similar to regex, but expand (like a command parameter would) the
    given expression before building a regex from the result.
    This highlights all the current search matches in italic:

---------------------------------------------
add-highlighter window dynregex '%reg{/}' 0:i
---------------------------------------------

== Specs highlighters

The following highlighters are useful to add indicators like lint warnings,
git blame output or spelling typos.
See <<options#types,`:doc options types`>> for the format of `line-specs`
and `range-specs`.

*flag_lines* <face> <option_name>::
    add columns in front of the buffer, and display the flags specified
    in `line-specs` option, using <face>.
    In this example two words will be added in the gutter: a blue Foo at
    line 1 and a bold red/yellow Bar on line 3:

----------------------------------------------------------------------
declare-option line-specs my_flags
set-option window my_flags "%val{timestamp}:1|Foo:3|{red,yellow+b}Bar"
add-highlighter window/ flag_lines blue my_flags
----------------------------------------------------------------------

*ranges* <option_name>::
    use the data in the `range-specs` option of the given name to highlight
    the buffer. The string part of each tuple of the range-specs is
    interpreted as a *face* to apply to the range.
    In this example the 3 first chars of the buffer will be colored in red:

--------------------------------------------------------
declare-option range-specs my_range
set-option window my_range "%val{timestamp}:1.1,1.3|red"
add-highlighter window/ ranges my_range
--------------------------------------------------------

*replace-ranges* <option_name>::
    use the data in the `range-specs` option of the given name to highlight
    the buffer. The string part of each tuple of the range-specs is
    interpreted as a *display line* to display in place of the range.
    Here, the 3 first chars of the buffer will be replaced by the word 'red':

--------------------------------------------------------
declare-option range-specs my_range
set-option window my_range "%val{timestamp}:1.1,1.3|red"
add-highlighter window/ replace-ranges my_range
--------------------------------------------------------

== Highlighting Groups

The *group* highlighter is a container for other highlighters. A subgroup
can be added to an existing group or scope using:

-----------------------------------
add-highlighter <path> group <name>
-----------------------------------

That group is then accessible using the *<path>/<name>* path

------------------------------------------------
add-highlighter <path>/<name> <type> <params>...
------------------------------------------------

In order to specify which kinds of highlighters can be added to a given group, the *-passes*
flag set can be passed along with the group name. Possible values for this option can be one
or several (separated with a pipe sign) of *colorize*, *move* or *wrap* (default: *colorize*):

--------------------------------------------------------------
add-highlighter window group -passes colorize|move|wrap <name>
--------------------------------------------------------------

== Regions highlighters

A special highlighter provides a way to segment the buffer into regions,
which are to be highlighted differently.

*name*::
    user defined, used to identify the region
*opening*::
    regex that defines the region start text
*closing*::
    regex that defines the region end text
*recurse*::
    regex that defines the text that matches recursively an end token
    into the region

The *recurse* option is useful for regions that can be nested, for example
the following contruct:

----------
%sh{ ... }
----------

accepts nested braces scopes ('{ ... }') so the following string is valid:

----------------------
%sh{ ... { ... } ... }
----------------------

This region can be defined with:

------------------------
shell_expand %sh\{ \} \{
------------------------

Regions are used in the region highlighters which can take any number
of regions.

The following command:

------------------------------------------------------
add-highlighter <path> regions <name> \
    <region_name1> <opening1> <closing1> <recurse1> \
    <region_name2> <opening2> <closing2> <recurse2>...
------------------------------------------------------

defines multiple regions in which other highlighters can be added as follows:

-----------------------------------------------
add-highlighter <path>/<name>/<region_name> ...
-----------------------------------------------

Regions are matched using the left-most rule: the left-most region opening
starts a new region. When a region closes, the closest next opening start
another region.

That matches the rule governing most programming language parsing.

Regions also supports a *-default <default_region>* switch to define the
default region, when no other region matches the current buffer range.

If the *-match-capture* switch is passed, then region closing and recurse
matches are considered valid for a given region opening match only if they
matched the same content for the capture 1.

Most programming languages can then be properly highlighted using a region
highlighter as root:

-----------------------------------------------------------------
add-highlighter <path> regions -default code <lang> \
    string <str_opening> <str_closing> <str_recurse> \
    comment <comment_opening> <comment_closing> <comment_recurse>

add-highlighter <path>/<lang>/code ...
add-highlighter <path>/<lang>/string ...
add-highlighter <path>/<lang>/comment ...
-----------------------------------------------------------------

== Shared Highlighters

Highlighters are often defined for a specific filetype, and it makes then
sense to share the highlighters between all the windows on the same filetypes.

Highlighters can be put in the shared scope in order to make them reusable.

---------------------------------------
add-highlighter shared/<group_name> ...
---------------------------------------

The common case would be to create a named shared group, and then fill it
with highlighters:

---------------------------------------
add-highlighter shared/ group <name>
add-highlighter shared/<name> regex ...
---------------------------------------

It can then be referenced in a window using the ref highlighter.

---------------------------------
add-highlighter window ref <name>
---------------------------------

The ref can reference any named highlighter in the shared scope.