md4c/test/spec-highlight.txt

# Highlight Spans

With the flag `MD_FLAG_HIGHLIGHT`, MD4C enables recognition of inline
highlight spans using the `==text==` syntax. A pair of equals signs on each
side wraps the content, which the HTML renderer outputs as `<mark>`.


## Basic recognition

```````````````````````````````` example
==Hello, world!==
.
<p><mark>Hello, world!</mark></p>
.
--fhighlight
````````````````````````````````

Highlight spans may appear inline alongside normal text:

```````````````````````````````` example
This is ==very important== text.
.
<p>This is <mark>very important</mark> text.</p>
.
--fhighlight
````````````````````````````````

Multiple independent highlight spans may appear in the same paragraph:

```````````````````````````````` example
==first== and ==second==
.
<p><mark>first</mark> and <mark>second</mark></p>
.
--fhighlight
````````````````````````````````


## Flag required

Without `MD_FLAG_HIGHLIGHT` the `==` sequence is treated as literal text:

```````````````````````````````` example
==highlight==
.
<p>==highlight==</p>
.
````````````````````````````````


## Nested inline spans

Emphasis inside a highlight span:

```````````````````````````````` example
==very *important* text==
.
<p><mark>very <em>important</em> text</mark></p>
.
--fhighlight
````````````````````````````````

Strong emphasis inside a highlight span:

```````````````````````````````` example
==**bold** and _italic_==
.
<p><mark><strong>bold</strong> and <em>italic</em></mark></p>
.
--fhighlight
````````````````````````````````

Inline code inside a highlight span:

```````````````````````````````` example
==highlighted `code`==
.
<p><mark>highlighted <code>code</code></mark></p>
.
--fhighlight
````````````````````````````````

A link inside a highlight span:

```````````````````````````````` example
==highlighted [link](http://example.com)==
.
<p><mark>highlighted <a href="http://example.com">link</a></mark></p>
.
--fhighlight
````````````````````````````````

A highlight span inside a link:

```````````````````````````````` example
[==highlighted link==](http://example.com)
.
<p><a href="http://example.com"><mark>highlighted link</mark></a></p>
.
--fhighlight
````````````````````````````````


## Whitespace rules

An equals delimiter cannot open a highlight span when immediately followed by
whitespace:

```````````````````````````````` example
== highlight==
.
<p>== highlight==</p>
.
--fhighlight
````````````````````````````````

An equals delimiter cannot close a highlight span when immediately preceded by
whitespace:

```````````````````````````````` example
==highlight ==
.
<p>==highlight ==</p>
.
--fhighlight
````````````````````````````````


## Delimiter length

Single equals signs are not highlight delimiters:

```````````````````````````````` example
=highlight=
.
<p>=highlight=</p>
.
--fhighlight
````````````````````````````````

Longer equals runs are not split into highlight delimiters:

```````````````````````````````` example
===highlight===
.
<p>===highlight===</p>
.
--fhighlight
````````````````````````````````


## Unmatched delimiters

An opening delimiter with no matching closer is literal:

```````````````````````````````` example
==highlight
.
<p>==highlight</p>
.
--fhighlight
````````````````````````````````

A closing delimiter with no matching opener is literal:

```````````````````````````````` example
highlight==
.
<p>highlight==</p>
.
--fhighlight
````````````````````````````````


## Paragraph boundary stops resolution

A highlight span cannot cross a paragraph boundary:

```````````````````````````````` example
This ==has a

new paragraph==.
.
<p>This ==has a</p>
<p>new paragraph==.</p>
.
--fhighlight
````````````````````````````````


## Suppression inside code

Equals signs inside code spans are treated as literal text:

```````````````````````````````` example
`==code==`
.
<p><code>==code==</code></p>
.
--fhighlight
````````````````````````````````

Equals signs inside fenced code blocks are treated as literal text:

```````````````````````````````` example
```
==code==
```
.
<pre><code>==code==
</code></pre>
.
--fhighlight
````````````````````````````````


## Interaction with other extensions

Highlight may appear inside a spoiler span:

```````````````````````````````` example
||==highlighted spoiler==||
.
<p><x-spoiler><mark>highlighted spoiler</mark></x-spoiler></p>
.
--fhighlight --fspoilers
````````````````````````````````

Highlight may appear inside strikethrough:

```````````````````````````````` example
~~==highlighted deletion==~~
.
<p><del><mark>highlighted deletion</mark></del></p>
.
--fhighlight --fstrikethrough
````````````````````````````````

Highlight may appear inside table cells:

```````````````````````````````` example
| Feature | Status |
| --- | --- |
| Highlight | ==done== |
.
<table>
<thead>
<tr><th>Feature</th><th>Status</th></tr>
</thead>
<tbody>
<tr><td>Highlight</td><td><mark>done</mark></td></tr>
</tbody>
</table>
.
--fhighlight --ftables
````````````````````````````````