Enable code prettifying for DS SE/fix these tags that have no default

It seems like code prettifying is not enabled for this SE. I came across this question and thought that the lack of syntax highlighting might just be because no default highlighter is defined for or (happened on SO once upon a time). I then went to edit it and tried adding the following highlighting tags to no effect:

# At the top of the document
<!-- language-all: python -->
<!-- language-all: py -->  # pretty sure this isn't a valid tag
<!-- language-all: lang-default -->

# At the top of a single code block
<!-- language: python -->
<!-- language: lang-default -->


If code prettifying isn't enabled across the SE, could we get it enabled? I realize this isn't an SE specifically for coding questions, but often a little code helps to explain a question succinctly, and having syntax highlighting makes code so much easier to read.

If it's just an issue with these tags, could we add the lang-default highlighter to the and tags?