Non-breakable start/end marks margin/padding/border space (even when it does not directly come from the associated layout box) <span style="padding: 5px"><span>nested content with padding parent</span</span> <nested content with padding parent> inline run has 5px non-breakable start/end.
Created attachment 355284 [details] Patch
Committed r238401: <https://trac.webkit.org/changeset/238401>
<rdar://problem/46186479>