I'd like to separate this issue to an independent bug, because there is an unsolved question on this behavior, see: https://lists.w3.org/Archives/Public/www-style/2015Nov/0193.html Depending on the answer there, the implementation could be easy or super complicated that we may only want an imperfect impl.

Bug 1224013 part 1 - Enable text-emphasis in UA sheets. The only usage of text-emphasis in UA sheets is to clear it on ruby text. Making it enabled in UA sheets allows that rule to take effect without additional code to reload html.css when the pref changes.

Bug 1224013 part 2 - Move leading fix to ruby base container. Per spec, the additional leading is added on side of ruby base container, not ruby container. This could lead to some trivial behavior changes on edge cases.

Bug 1224013 part 3 - Render text-emphasis outside ruby.

Bug 1224013 part 4 - Add reftests for text-emphasis with ruby.

Comment on attachment 8694160 [details] MozReview Request: Bug 1224013 part 1 - Enable text-emphasis in UA sheets. https://reviewboard.mozilla.org/r/26667/#review24207 It might be worth putting a note on the bug to enable these properties that you can remove these flags when you remove the pref. (If there's not a bug to enable them already, there should be... with bugs blocking it.)

Comment on attachment 8694161 [details] MozReview Request: Bug 1224013 part 2 - Move leading fix to ruby base container. https://reviewboard.mozilla.org/r/26669/#review24409

Comment on attachment 8694162 [details] MozReview Request: Bug 1224013 part 3 - Render text-emphasis outside ruby. https://reviewboard.mozilla.org/r/26671/#review24429

Comment on attachment 8694163 [details] MozReview Request: Bug 1224013 part 4 - Add reftests for text-emphasis with ruby. https://reviewboard.mozilla.org/r/26673/#review24431

https://hg.mozilla.org/integration/mozilla-inbound/rev/9dfd459c839628fc852a8beaf2fb599b28269dd2 Bug 1224013 part 1 - Enable text-emphasis in UA sheets. r=dbaron https://hg.mozilla.org/integration/mozilla-inbound/rev/15113b4231c70ccbc1ce420fd03f1984c5b89d22 Bug 1224013 part 2 - Move leading fix to ruby base container. r=dholbert https://hg.mozilla.org/integration/mozilla-inbound/rev/5c44af8f7d6ee6319fb5d82970c8811383036ea9 Bug 1224013 part 3 - Render text-emphasis outside ruby. r=jfkthame https://hg.mozilla.org/integration/mozilla-inbound/rev/b0b15e5ed2712aa171dd39ba98a42e831f0d7b1d Bug 1224013 part 4 - Add reftests for text-emphasis with ruby. r=jfkthame

https://hg.mozilla.org/integration/mozilla-inbound/rev/835de4b7bcb2b9016ef425db25878929c28a9448 Backed out 8 changesets (bug 1225018, bug 1229278, bug 1224013) for reftest failures on CLOSED TREE

So part 2 breaks the reftests because when the ruby base container is placed, its required leadings have not been figured out. I'm going to land the patches except part 2 (also change part 3 to find nearest ruby frame instead of ruby base container).

https://hg.mozilla.org/integration/mozilla-inbound/rev/ddf13e6aa97ef9585b9d06deab3ee9b1e0ce81d3 Bug 1224013 part 1 - Enable text-emphasis in UA sheets. r=dbaron https://hg.mozilla.org/integration/mozilla-inbound/rev/5f5ca882d872a71622cc305bc25a31fb5fc7ca79 Bug 1224013 part 2 - Render text-emphasis outside ruby. r=jfkthame https://hg.mozilla.org/integration/mozilla-inbound/rev/3714873643124a5c65c938366db4eba3fc9cbcb4 Bug 1224013 part 3 - Add reftests for text-emphasis with ruby. r=jfkthame

https://hg.mozilla.org/mozilla-central/rev/ddf13e6aa97e https://hg.mozilla.org/mozilla-central/rev/5f5ca882d872 https://hg.mozilla.org/mozilla-central/rev/371487364312