Code Editor: Linter (HTMLHint) should show error if checkbox doesn't have associated <label>

[shooper]

The Custom HTML Linter should show an error if an checkbox field does not have an associated label element. This would be a good improvement for accessibility.

To reproduce:

1. Create a custom HTML widget
2. Enter the following code:

<input type="checkbox"> Checkbox Label

3. No warning/error appears.

[westonruter]

You could write a custom ​HTMLHint rule to enforce this, but a warning is probably better than an error.

[afercia]

Discussed during today's accessibility bug-scrub. Yes it would be great to have the linter warn for accessibility errors, not just the ones related to a checkbox though :) Will defer the decision to the editor and widgets teams, as we're not even sure it's technically feasible.

[netweb]

There's a pull request for HTMLHint already created, sadly not merged for this:

• Rule: input-requires-label ​https://github.com/yaniswang/HTMLHint/pull/159

Unfortunately, it appears the HTMLHint project is unmaintained for now, there's been ​no response from the maintainer in ~6 months, there are quite a few forks though I'm not sure if it would be possible to use a fork

[sabernhardt]

That ​pull request was merged in HTMLHint earlier this year.

[sabernhardt]

The current HTMLHint version included in WordPress is 0.9.14, and the first version with the label-checking feature was 0.13.0

[joedolson]

I'm highly favorable to having improvements that can help guide users better. It looks like HTMLHint has been updated quite a bit in the last few years, and it's worth looking at updating this.

I'm going to milestone this for 6.8, and look into updating HTLMHint.

[joedolson]

Since this updates a major library used in core, I think this should probably be marked as early.

[audrasjb]

As the ticket is marked early and don't have any patch yet, let's move it to Future Release.

Trac ticket: https://core.trac.wordpress.org/ticket/42780