Suggested solution: Change lines 1520/1521 to

8.2.4

'bdo' => $common,

There is more weird stuff happening. I hope the following is complete:

• <bdo> accepts no attributes; should accept $common
• <br> accepts just "id", "class", "title", "style" and "clear"; should accept $common and "clear" (not allowing some of these is an ancient HTML 4 restriction)
• <q> accepts no attributes; should accept $common and "cite"
• <span> accepts $block; should accept just $common (the difference is <span align="...">, which was never legal and doesn't work)
• <wbr> accepts just "id", "class", "title" and "style"; should accept $common (restriction was apparently copied from <br>)

Patches accepted. :-) You can read [[mw:Gerrit]] for help.

Created attachment 13477
Proposed additions to and removals from the attribute whitelist

This is completely untested. I have never worked with the PHP code.

Attached:

Bugzilla doesn't show the prose at the beginning of the .diff file, so here it is:

Bug 55582: Put the HTML attribute whitelist closer to HTML5

• Add the global attributes to <bdo> and <q> and add "cite" to <q>. This is to make these elements actually usable: <bdo> needs a "dir" attribute to be useful for anything, and the whole point of <q> compared to hard-coded quotation marks is its support for the "lang" and "cite" attributes.
• Drop the "align" attribute from <span> because it was never standards-compliant and does not work in browsers either, unless one constructs such unlikely things as <span align="center" style="display:block;">.
• Drop the obsolete "char" and "charoff" attributes from <tr>, <td>, <th>. These have not been implemented in browsers anyway.
• Drop the obsolete presentational attributes "align", "valign" and "width" from <colgroup>, <col>, <thead>, <tfoot> and <tbody>. These elements are currently not accepted in wikitext anyway, but removing these attributes from the whitelist ensures that they are not accidentally enabled in the future.
• Drop the obsolete presentational attributes "noshade" and "size" from <hr>. They have been overridden by skin-specific CSS for a long time anyway.
• Allow all global attributes on <br> and <wbr>. Not allowing "dir" and "lang" on <br> was a restriction in HTML 4.01, presumably copied to <wbr>, that has been lifted in HTML5. Allowing these may not be particularly useful, but simplifies the code.

Change 89384 had a related patch set uploaded by PleaseStand:
Put the HTML attribute whitelist closer to HTML5

https://gerrit.wikimedia.org/r/89384

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Change 89384 merged by jenkins-bot:
Put the HTML attribute whitelist closer to HTML5

https://gerrit.wikimedia.org/r/89384

I merged the patch into master. Please, get a developer account to make everybody's lives easier :)