https://drafts.csswg.org/css-text-3/#white-space-processing "Unsupported Default_ignorable characters must be ignored for text rendering." As mentioned in 245154@main, taking zero width glyphs (e.g. control characters) into consideration while collecting fallback font information may result in incorrect line height and baseline positioning; an alternative mentioned in 245154@main was to check against unicode ranges to omit certain glyphs. 246121@main fixed a regression in which bidi control chars rendered, and replaced our previous hardcoded list of Default_ignorable characters with the helper function,FontCascade::isCharacterWhoseGlyphsShouldBeDeletedForTextRendering (also refactored in 260081@main). That helper function covers the use case 'rightToLeftOverride' which the test `LayoutTests/fast/text/fallback-font-and-zero-width-glyph.html`, currently marked as failing in glib, relies on.
PR, WIP. https://github.com/WebKit/WebKit/pull/14240
Committed 264509@main (07b1f5f81cef): <https://commits.webkit.org/264509@main> Reviewed commits have been landed. Closing PR #14240 and removing active labels.
<rdar://problem/109820978>