When creating footnotes with the PHP Markdown Extra parser, the id attributes are first correctly generated (e.g. fnref:1 and fn:1) but then they are changed inside Xss:filter(), where fnref: and fn: are treated as unsafe URL protocols and stripped away.
1. Configure to use Markdown with the PHP Markdown Extra parser
2. Create content with footnotes, e.g:
This is some text with a footnote.[^1] [^1]: And that's the footnote.
3. Save and examine the HTML output.
Not sure. It looks like colons are not really recommended in id attributes to begin with, but that is up to the parser library. The treatment of colons in Xss::filter() doesn't seem to be configurable.
Would it be reasonable to change any colon preceded by fn(ref)?[0-9]* into underscores or so, before calling Xss:filter()?
We might change how some id attributes in the output HTML will look like.
Needs review
3.0
Parser: PHP Markdown/PHP Markdown Extra
Created a merge request with an implementation of my suggestion of changing fn:1 etc into fn_1.
(I'm new to working with merge requests on Drupal.org, so apologies if I'm doing it wrong!)