Allow the use of tabs for list indents and outdents

[DevinWalker]

PR Overview

Allow tab to be used to indent list items. As well, allow shift + tab to outdent tabs.

Preview

Ref: #1552 and #1640

[afercia]

As mentioned in #1552 this would break keyboard navigation through blocks 🚨 Once in a "list" block there's no way to tab away from the block, since the Tab key is used for indentation.

[swissspidy]

@afercia Unless we fix #1482 first.

[afercia]

Unless we fix #1482 first.

Yep but then it would be unexpected that tabbing works for some blocks and doesn't for some other ones?

[ellatrix]

Worth noting that this breaks in TinyMCE as well. Tab will normally focus the next focusable element, except in lists. Not sure what the solution is here. Could it work only at the start of a list item, and use wp speak to alert the user?

Just tried it in Google Docs and there it also only works at the start of a list item. Everywhere else it inserts an actual tab character.

[afercia]

Yep this always worked this way in TinyMCE too. However, in TinyMCE there are no "blocks" so it is always possible to enter some content after the list (even just a space) and the Tab key switches back to its default action.

[BoardJames]

We added the lists_indent_on_tab option to TinyMCE specifically to turn it off for the list block to address the usability problem of it being a tab trap. There are now keyboard shortcuts for indenting and outdenting ( ctrl/command + ] for indent and ctrl/command + [ for outdent ).

[BoardJames]

See #1826

[gziolo]

We added the lists_indent_on_tab option to TinyMCE specifically to turn it off for the list block to address the usability problem of it being a tab trap. There are now keyboard shortcuts for indenting and outdenting ( ctrl/command + ] for indent and ctrl/command + [ for outdent ).

It looks like using new keyboard shortcuts is the way to go here. @DevinWalker thanks for spending time on this PR. I'm closing it, but feel free to reopen if you think it's still an issue.

[afercia]

ctrl/command + ] for indent and ctrl/command + [ for outdent should be tested also on non-English layout keyboards. For example, the Italian keyboard layout: