"If the inline box contains no glyphs at all, or if it contains only glyphs from fallback fonts, it is considered to contain a “strut” (an invisible glyph of zero width) with the metrics of the box’s first available font."
Created attachment 416799 [details] Patch
Created attachment 416821 [details] Patch
Committed r271096: <https://trac.webkit.org/changeset/271096> All reviewed patches have been landed. Closing bug and clearing flags on attachment 416821 [details].
<rdar://problem/72691035>