HeadingPermalinkExtension does not percent-encode CJK names, but commonmark does percent-encode CJK URLs

[ptmkenny]

Version(s) affected

2.4.2

Description

This is an edge case, but when you have a relative link with CJK text and the HeadingPermalinkExtension enabled, then the relative link gets percent-encoded (because Commonmark percent-encodes links), but the name that the relative link is pointing to remains the original CJK text.

This is a minor issue because the link works. However, it can cause automated tests like pa11y to fail because the relative link is pointing to a percent-encoded name, but the name is not percent encoded.

How to reproduce

Here is a link: [Go to summary](#まとめ)

## まとめ

Summary

Produces:

<p>Here is a link: <a href="#%E3%81%BE%E3%81%A8%E3%82%81">Go to summary</a></p>
<h2 name="まとめ">まとめ</h2>
<p>Summary</p>

Possible solution

I know this is a minor issue, but for the sake of consistency I think it would be great to percent-encode the CJK in the names processed by HeadingPermalinkExtension in the same manner as links.

Additional context

• Related thread on similar issue for commonmark, conclusion was percent-encoding is the approach to take: CJK link processing causes Markdown links and HTML links to have different URLs commonmark/commonmark-spec#672

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