HTML parsing issue in handbooks

[samuelsidler]

The handbooks menu in the sidebar (e.g. "Contents" on ​make/themes) shows the following code:

<h1 class="widget-title">Contents</h2>

Note the error? Okay, there's two:

1. The opening and closing tags should match.
2. The headings shouldn't be an <h1> at all, for accessibility purposes.

[SergeyBiryukov]

The opening tag is in WPorg_Handbook::handbook_sidebar()​, and the closing tag is in WPorg_Handbook_Pages_Widget::widget()​.

<h1> was introduced in [3686], register_sidebar() default is <h2 class="widgettitle">.

meta-2371.patch​ changes it back to <h2>.

[samuelsidler]

Does it make sense as an <h2> even? Or should it be something more like a <nav>?

[coffee2code]

In 4626:

Handbook plugin: Use h2 as tag for widget titles instead of h1.

Props SergeyBiryukov.
Fixes #2371.

[coffee2code]

@samuelsidler: I wouldn't say the sidebar header should be <nav>, though a <nav> could be used to wrap the <ul> containing the widget's links (optionally including the <h2> widget header).

[coffee2code]

This was undone by @pento in [4690], which reintroduces the mismatch widget title tags for the table of contents as reported here.

Naturally, that can be fixed while still retaining the revert that happened, but @samuelsidler expressed a desire not to use h1 for the widget title.

Also, the use of h1 messes up the style of the table of contents (aka "Chapters") title for DevHub handbooks (again, styling can be changed there if we're sticking with h1).

What was the reason for having h1 as the widget title tag instead of h2? (I'm assuming for o2, so I mean more specifically than that.)

[samuelsidler]

I'm guessing @pento had a change in his sandbox and overwrote the fix here by accident. :)

[SergeyBiryukov]

The revert of [4626] in [4690] looks accidental to me as well.

[pento]

In 4695:

Handbook: [4690] accidentally reverted [4626]. This commit reverts the revert part of that commit, reverting to the correct behaviour.

See #2371.