[Docs] (Apache config) Headers *can* match based on Content-Type

[Malvoz]

no-html-only-headers states "Because mod_headers cannot match based on the content-type [...]", however this is untrue, using expr in apache 2.4.10 and later.

Here's one example method:

Header set X-Header "Value" "expr=%{CONTENT_TYPE} =~ m#{MIME-Type}#i"

and I believe to match multiple types you'd do:
expr=%{CONTENT_TYPE} =~ m#text/html|application/pdf|{etc...}#i

FWIW, H5BP switched to using expr from <FilesMatch> in their snippets.