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mirror of https://github.com/vim/vim.git synced 2025-07-26 11:04:33 -04:00
Aliaksei Budavei dc7ed8f946
runtime(html): Optionally fold tags with the "expr" method
Tag folding poses a few difficulties.  Many elements, e.g.
"blockquote", are always delimited by start and end tags;
end tags for some elements, e.g. "p", can be omitted in
certain contexts; void elements, e.g. "hr", have no end tag.
Although the rules for supporting omissible end tags are
ad-hoc and involved, they apply to elements in scope.
Assuming syntactical wellformedness, an end tag can be
associated with its nearest matching start tag discoverable
in scope and towards the beginning of a file, whereas all
unbalanced tags and inlined tags can be disregarded.

For example:
------------------------------------------------------------
<!DOCTYPE html>
<html lang="en">		<!-- >1 : 1 -->
  <body>			<!-- >2 : 2 -->
    <p>Paragraph #1.		<!--  = : 2 -->
    <p>				<!-- >3 : 3 -->
      Paragraph #2.		<!--  = : 3 -->
    </p>			<!-- <3 : 3 -->
    <p>Paragraph #3.</p>	<!--  = : 2 -->
  </body>			<!-- <2 : 2 -->
</html>				<!-- <1 : 1 -->
------------------------------------------------------------

(HTML comments here, "<!-- ... -->", record two values for
each folded line that are separated by ":", a value obtained
from "&foldexpr" and a value obtained from "foldlevel()".)

Innermost foldedable tags will be flattened.  For example:
------------------------------------------------------------
<!DOCTYPE html>
<html lang="en">		<!-- >1 : 1 -->
  <body>			<!-- >2 : 2 -->
    <div class="block">		<!-- >3 : 3 -->
      <pre><code>		<!-- >4 : 4 -->
[CODE SNIPPET]			<!--  = : 4 -->
      </code></pre>		<!-- <4 : 4 -->
    </div>			<!-- <3 : 3 -->
  </body>			<!-- <2 : 2 -->
</html>				<!-- <1 : 1 -->
------------------------------------------------------------

No folding will be requested for the "<code>"-"</code>" tag
pair and reflected by "&foldexpr" because such a fold would
have claimed the same lines that the immediate fold of the
"<pre>"-"</pre>" tag already claims.

Run-on folded tags may confuse Vim.  When a file such as:
------------------------------------------------------------
<!DOCTYPE html>
<html lang="en">		<!-- >1 : 1 -->
  <body>			<!-- >2 : 2 -->
    <div class="block">		<!-- >3 : 3 -->
      <pre>			<!-- >4 : 4 -->
	<code>			<!-- >5 : 5 -->
[CODE SNIPPET #1]		<!--  = : 5 -->
	</code>			<!-- <5 : 5 -->
      </pre>			<!-- <4 : 4 -->
    </div>			<!-- <3 : 3 -->
				<!--  = : 3 -->
    <div class="block">		<!-- >3 : 3 -->
      <pre>			<!-- >4 : 4 -->
	<code>			<!-- >5 : 5 -->
[CODE SNIPPET #2]		<!--  = : 5 -->
	</code>			<!-- <5 : 5 -->
      </pre>			<!-- <4 : 4 -->
    </div>			<!-- <3 : 3 -->
  </body>			<!-- <2 : 2 -->
</html>				<!-- <1 : 1 -->
------------------------------------------------------------

is reformatted as follows:
------------------------------------------------------------
<!DOCTYPE html>
<html lang="en">		<!-- >1 : 1 -->
  <body>			<!-- >2 : 2 -->
    <div class="block">		<!-- >3 : 3 -->
      <pre>			<!-- >4 : 4 -->
	<code>			<!-- >5 : 5 -->
[CODE SNIPPET #1]		<!--  = : 5 -->
	</code>			<!-- <5 : 5 -->
      </pre>			<!-- <4 : 4 -->
    </div><div class="block"><pre><code> <!-- <3 : 3 -->
[CODE SNIPPET #2]		<!--  = : 2 ? -->
	</code>			<!-- <5 : 2 ? -->
      </pre>			<!-- <4 : 2 ? -->
    </div>			<!-- <3 : 2 ? -->
  </body>			<!-- <2 : 2 -->
</html>				<!-- <1 : 1 -->
------------------------------------------------------------

"&foldexpr" values will not be used as is for the lines
between (and including) "[CODE SNIPPET #2]" and "</div>".
(Cf. v9.1.0002.)

Having syntax highlighting in effect, tag folding using the
"fold-expr" method can be enabled with:
------------------------------------------------------------
	let g:html_expr_folding = 1
------------------------------------------------------------

By default, tag folding will be redone from scratch after
each occurrence of a TextChanged or an InsertLeave event.
Such frequency may not be desired, especially for large
files, and this recomputation can be disabled with:
------------------------------------------------------------
	let g:html_expr_folding_without_recomputation = 1
        doautocmd FileType
------------------------------------------------------------

To force another recomputation, do:
------------------------------------------------------------
	unlet! b:foldsmap
	normal zx
------------------------------------------------------------

References:
https://web.archive.org/web/20250328105626/https://html.spec.whatwg.org/multipage/syntax.html#optional-tags
https://en.wikipedia.org/wiki/Dangling_else

closes: #17141

Signed-off-by: Aliaksei Budavei <0x000c70@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
2025-05-10 21:40:41 +02:00
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This directory contains Vim scripts for syntax highlighting.

These scripts are not for a language, but are used by Vim itself:

syntax.vim	Used for the ":syntax on" command.  Uses synload.vim.

manual.vim	Used for the ":syntax manual" command.  Uses synload.vim.

synload.vim	Contains autocommands to load a language file when a certain
		file name (extension) is used.  And sets up the Syntax menu
		for the GUI.

nosyntax.vim	Used for the ":syntax off" command.  Undo the loading of
		synload.vim.

The "shared" directory contains generated files and what is used by more than
one syntax.


A few special files:

2html.vim	Converts any highlighted file to HTML (GUI only).
colortest.vim	Check for color names and actual color on screen.
hitest.vim	View the current highlight settings.
whitespace.vim  View Tabs and Spaces.


If you want to write a syntax file, read the docs at ":help usr_44.txt".

If you make a new syntax file which would be useful for others, please send it
to the vim-dev mailing list <vim-dev@vim.org>.  Include instructions for
detecting the file type for this language, by file name extension or by
checking a few lines in the file. And please write the file in a portable way,
see ":help 44.12".

If you have remarks about an existing file, send them to the maintainer of
that file.  Only when you get no response send a message to the vim-dev
mailing list: <vim-dev@vim.org>.

If you are the maintainer of a syntax file and make improvements, send the new
version to the vim-dev mailing list: <vim-dev@vim.org>

For further info see ":help syntax" in Vim.