Make unicode-bidi: isolate the default for elements with a dir attribute (mozilla)

[r12a]

https://bugzilla.mozilla.org/show_bug.cgi?id=1218706

Xidorn Quan :xidorn 2015-10-27 02:03:58 PDT

The HTML5 spec changes the semantics of the dir attribute to use unicode-bidi:isolate instead of unicode-bidi:embed (on all elements except BDO), and unicode-bidi: isolate-override instead of unicode-bidi:bidi-override on BDO.

Here is a link to the relevant section of the HTML5 spec and the CSS involved:
http://www.w3.org/TR/html5/rendering.html#bidi-rendering

Similarly, the definition of the dir attribute in the HTML5 spec speaks of it making the element's content "directionally isolated"; see http://www.w3.org/TR/html5/dom.html#the-dir-attribute

This is a very important change that should make it easier to author bidi pages. It was proposed and extensively discussed by the W3C i18n WG (http://www.w3.org/International/wiki/Html-bidi-isolation), and then by the WHATWG and HTML5 WG (https://www.w3.org/Bugs/Public/show_bug.cgi?id=23260).

It is also a very easily implemented change - just a change in the default CSS.

The change is not backward compatible, but it is very close to the behavior of IE 8 through IE 11. The bodies mentioned above were well aware of the lack of backward compatibility, but approved the change nonetheless because of its benefits going forward.

It is now the standard.

Firefox's implementation of unicode-bidi:isolate (prefixed as -moz-isolate) has at least passed all tests in l18n wg. But we do still have some issues with isolate-override currently.

Related issue for Chrome: https://code.google.com/p/chromium/issues/detail?id=391260
Related issue for WebKit: https://bugs.webkit.org/show_bug.cgi?id=134630

Today, I discussed with Richard Ishida (from L18N WG), Koji Ishii (from Blink team), and Myles C. Maxfield (from WebKit team). No one had idea how many pages would be broken, and we didn't even have idea how this breakage could be measured. But we thought this is a good change we probably should go forward.

[r12a]

Now marked Fixed. Should hopefully appear in v47.