[ticket/16984] Accessibility - fix tab order for keyboard navigation

[lionel-rowe]

Fixes PHPBB3-16984: Accessibility — confusing tab order for keyboard navigation

This is a blanket regex find-and-replace of tabindex=(['"]?)[1-9]\d*\1 for tabindex=$10$1 to bring the HTML in-line with the Web AIM guidance:

Important
tabindex values of 1+ must be avoided. These elements will receive keyboard focus before elements with no tabindex value (or tabindex="0") resulting in a navigation order that is different from the visual and/or screen reader order. Instead of using tabindex, simply adjust the page's source code order to support a logical navigation and reading order, then use CSS to adjust the visual presentation.

The source code already uses a logical navigation and reading order, so the fix is simple 😊

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Checklist:

• Correct branch: master for new features; 3.3.x for fixes
• Tests pass
• Code follows coding guidelines: master and 3.3.x
• Commit follows commit message format

Tracker ticket (set the ticket ID to your ticket ID):

https://tracker.phpbb.com/browse/PHPBB3-16984

[marc1706]

If I read this correctly, the cleaner approach would probably be to completely remove the tabindex? In that case I'd actually then opt for removing it instead of setting it to 0.

[lionel-rowe]

@marc1706 Lack of tabindex isn't always equivalent to tabindex=0:

<!-- `tabindex` can safely be removed, as `input` is already focusable by default -->
<input type="submit" tabindex="0">

<!-- `div` is not usually focusable, so removing `tabindex` would prevent element from being focused -->
<div class="fake-button" tabindex="0"></div>

As most/all of these are inputs though, should be OK to remove — I'll do some testing and see if anything breaks.