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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.

== General highlighters

*regex* <ex> <capture_id>:<face> ...::
    highlight a regex, takes the regex as first parameter, followed by
    any number of face parameters. For example:

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

    will highlight C++ style comments in cyan, with an eventual 'TODO:'
    in yellow on red background

*dynregex*::
    Similar to regex, but expand (like a command parameter would) the
    given expression before building a regex from the result

*flag_lines* <face> <option_name>::
    add a column in front of the buffer, and display the flags specified
    in <option_name>, using <face>

*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, 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.

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

*ranges* <option_name>::
    use the data in the range-specs option of the given name to highlight
    the buffer. The string part of the is interpretted as a face to apply
    to the 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 the is interpretted as a display line to
    display in place of the range.

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

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

== Highlighting Groups


The *group* highlighter is a container for other highlighters. You can add a
a subgroup 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.

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

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

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

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

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

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