Highlight

Overview

Highlight is an extension that adds support for code highlighting. Its purpose is to provide a single place to configure syntax highlighting for code blocks. Both InlineHilite and SuperFences can use Highlight to configure their highlight settings, but Highlight will also run all non-fence code blocks through the highlighter as well.

The Highlight extension is inspired by CodeHilite, but differs in features. PyMdown Extensions chooses not to implement special language headers for standard Markdown code blocks like CodeHilite does; PyMdown Extensions takes the position that language headers are better suited in fenced code blocks. So standard Markdown code blocks will just be styled as plain text unless guess_language is enabled. If you wish to highlight lines and define line numbers per code block, it is advised to use the SuperFences extension.

The Highlight extension can be included in Python Markdown by using the following:

import markdown
md = markdown.Markdown(extensions=['pymdownx.highlight'])

Syntax Highlighting

If Pygments is installed, it will be the default syntax highlighter, but if it is not, or if use_pygments is turned off, code tags will be rendered in the HTML5 format for JavaScript highlighting:

<pre class="highlight"><code class="language-mylanguage"></code></pre>

highlight is the default class name, and will be applied to code blocks, whether Pygments is disabled or not. This class name can be changed with the css_class option.

By default, the prefix language- is applied to language classes when Pygments is disabled or when Pygments code blocks enable language classes via pygments_lang_class. This prefix can be changed via the language_prefix option.

The language class, and any attributes added via the attr_list extension, are added to the <code> element. The code_attr_on_pre option will force them to be attached to the <pre> element.

All other options specifically control the Pygments highlighter and will have no affect if Pygments usage is disabled.

Extended Pygments Lexer Options

If using Pygments, some lexers have special settings. For instance, the php lexer has the option startinline which, if enabled, will parse PHP syntax without requiring <? at the beginning. Highlight allows you to configure these settings via the option extend_pygments_lang.

extend_pygments_lang allows you to create a special Pygments alias language where you can configure the language settings to your liking. So if you wanted to enable startinline for php, you might create a language alias called php-inline that maps to php with startinline enabled. This would allow you to use php for normal PHP blocks, but also allow you to do use php-inline for code without specifying <?. You can also use extend_pygments_lang to completely override the base language's options – assuming your specified name overrides an existing name.

extend_pygments_langis an array of dictionaries. Each dictionary contains three keys: name which is the new name you are adding, lang which is the language the new name maps to, and options which is a dictionary of the options you wish to apply.

`#!php-inline $a = array("foo" => 0, "bar" => 1);`

extend_pygments_lang = [
    {"name": "php-inline", "lang": "php", "options": {"startinline": True}}
]

Preserve Leading/Trailing Newlines

It is not uncommon for Markdown parsers to preserve both leading and trailing newlines in things like fenced code. This doesn't usually happen for indented code blocks.

To be clear the SuperFences extension does not strip leading and trailing new lines, this is the default behavior of the Pygments syntax highlighter, not the SuperFences extension's parsing logic. When Pygments is disabled, both leading and trailing newlines are preserved.

While it is rare for people to actually need leading and trailing newlines, if such behavior was desired, it can be retained by disabling the stripnl option in Highlight which will ensure that all Pygments lexers have this option disabled.

Inline code blocks, such as those provided by InlineHilite, will be unaffected. Indented code blocks will also not be affected as leading and trailing newlines are never retained in indented code blocks.

Line Number Styles

Pygments has two available styles when outputting source code with line numbers enabled: table and inline. table is the default output and creates a table output for lines with numbers. inline places the line numbers directly in the source code output and can sometimes be undesirable as copy and paste will always copy the line numbers as well.

The Highlight extension provides a third line number style called pymdownx-inline. Instead of writing line numbers directly in the pre like Pygments' default inline style does, it writes the line numbers as <span class="lineno" data-linenos="1 "></span>. This way the line numbers are un-selectable and can be displayed with CSS:

[data-linenos]:before {
  content: attr(data-linenos);
}

Line number styles are set with the option linenums_style as described in Options.

Options

All options below control the Pygments' output. The three exceptions are use_pygments which disables Pygments, css_class which sets the name of the class assigned to the generated code blocks, and code_attr_on_pre which only apply when Pygments is disabled. Many of these options are demonstrated in the SuperFences documentation.