It seems asking the question helped me to answer it!
You can use the Liquid contains
in order to look for a pattern in your post.
For example, if the included pattern.html
contains a particular piece of code (<!--pattern-->
for instance, or any particular HTML), you can use in your head:
<!doctype html>
<html>
<head>
{% if content contains "<!--pattern-->" %} code here {% endif %}
</head>
<body>
{{ content }}
</body>
</html>
This can be used for any HTML pattern. For example, if you want to call the CSS file producing syntaxic coloration only if there is code in the page, use:
<!doctype html>
<html>
<head>
{% if content contains "<code>" %}
<link rel="stylesheet" href="code.css">
{% endif %}
</head>
<body>
{{ content }}
</body>
</html>