In the following answer I've inserted this language hint
<!-- language-all: lang-html -->
However, it is not picking it up and therefore not formatting it with HTML syntax colours.
https://security.stackexchange.com/a/65467/8340
Is there any reason why? I have tried just language before each block as well to no avail.
Syntax highlighting is not turned on for Security.se.
We do not usually turn it on for sites that do not have a majority of posts with code in them (Lego, cooking, RPG are examples of such sites). Security tends to have more prose than code - hence, it isn't turned on.
The reason for this is that turning it on means including more JavaScript and slows everything down - performance matters to us.
Use <!-- language-all: lang-or-tag --> to use the given highlighting for all the following code blocks.