Created attachment 8633217 [details] testcase ###!!! ASSERTION: Negative descent???: 'aMetrics.BSize(aMetrics.GetWritingMode()) - aMetrics.BlockStartAscent() >= 0', file layout/generic/nsTextFrame.cpp, line 8540
Submitted a proposal to CSSWG for forcing writing-mode on ruby internal boxes. If that proposal gets accepted, this assertion could be fixed easily.
The proposal email: https://lists.w3.org/Archives/Public/www-style/2015Jul/0165.html
To fix this bug, we may need to wrap the content inside ruby base / ruby text in an anonymous block if the content has an orthogonal writing mode.
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