it's an inline box specific term.
Created attachment 463210 [details] Patch
Created attachment 463240 [details] Patch
Created attachment 463268 [details] [fast-cq]Patch
Committed 256061@main (71726246b913): <https://commits.webkit.org/256061@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 463268 [details].
<rdar://problem/101630436>