In bug 1218706, we applied "unicode-bidi: isolate" too all elements with dir attribute except bdo. bdo needs "isolate-override", which we haven't fully supported yet, but once we finish that, we should change its default value.

What's missing in isolate-override support? I added it (prefixed) in bug 774335, and it's already used in html.css for bdo[dir="auto"]

Ah, I didn't notice it is already there for bdo[dir="auto"]. Then I guess we should make it the default for "bdo, bdo[dir]" directly. The issue is that, we are still failing tests of isolate-override from CSSWG. It can be seen here: [1]. I compiled a build with unprefixed unicode-bidi values, and ran through the test suite, so the tests in this list which has one "passed" but lots of "failed" are likely due to that. The tests with absolutely no "passed" are the problems we have. So it's bidi-isolate-override-005 ~ 010 for isolate-override. [1] https://test.csswg.org/harness/results/css-writing-modes-3_dev/grouped/section/2/

Review commit: https://reviewboard.mozilla.org/r/61788/diff/#index_header See other reviews: https://reviewboard.mozilla.org/r/61788/

Comment on attachment 8767084 [details] Bug 1249497 - Use isolate-override for bdo elements. https://reviewboard.mozilla.org/r/61788/#review58556

Pushed by xquan@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/d42940726072 Use isolate-override for bdo elements. r=jfkthame

Updated the site compat doc: https://www.fxsitecompat.com/en-CA/docs/2016/elements-with-dir-attribute-will-have-unicode-bidi-isolate/

Added an info in: https://developer.mozilla.org/en-US/Firefox/Releases/50#HTML I don't think it is worth a mention on the element page itself.