Focus: Always jump to URL hashes

[EricDunsworth]

When visiting a hash link (#id), WET's focus plugin checks whether the destination is situated within a closed details element or tab panel. If so, the plugin automatically expands the destination's details element or tab panel. The plugin subsequently focuses onto the destination.

However, that sometimes causes inconsistent scrolling behaviour. Scrolling will work differently depending on if the link's destination is in the same page or on a separate page.

If a user visits a same-page hash link whose destination is in a closed details element/tab panel, everything works as expected. The plugin will expand the parent and the browser will jump to the destination. The destination will appear at the top of the browser viewport.

If a user visits a hash link whose destination is on a separate page, the plugin will run... but won't jump to the destination. Instead of jumping, the browser will scroll to show the destination at the bottom (Gecko/Trident) or the middle (Blink/Webkit) of the viewport. This is due to the focus plugin causing browsers to incorrectly use their natural focus scrolling behaviour in this context.

This commit corrects that behaviour by adding a flag to always navigate to hashes that are being focused on. As a result, browsers can use their natural link jumping behaviour. It also doesn't add anything to the browser's navigation history (since the hash was already in the page's URL beforehand).

[EricDunsworth]

Marked as a draft since I ran into some strange behaviour in Edge Trident. It's showing a dotted border or outline when jumping to in-page URL hashes, but not when coming from a separate page. Some other browsers I tested in show outlines, but do it consistently for both in-page and separate page hash links.

[duboisp]

Can you add a working example page of the auto-expand summary element when linked through an anchor?

[duboisp]

I am suggesting to use "fragment" instead

ref. Section 3 in this doc: https://tools.ietf.org/html/rfc3986