Hi,
I’ve been working with Claude on a Kerning issue in Hebrew on browsers. After getting its help with fixing the issue I want to report it here so it’ll hopefully be fixed or at least help others. I asked Claude to write the report so the description is as accurate as possible 
Here’s Claude’s text:
I’ve discovered two bugs in Glyphs 3’s RTL kerning export that prevent Hebrew kerning from working in web browsers:
Bug 1: Missing RightToLeft flag in GPOS lookup
When exporting fonts with Hebrew kerning (set in RTL mode), the Hebrew kerning lookup is exported with LookupFlag value=“8” (ignoreMarks only). It should be LookupFlag value=“9” (ignoreMarks + RightToLeft). Without the RightToLeft flag, browsers don’t apply the kerning to RTL text.
Bug 2: kern feature not registered for IWR language system
The kern feature is only registered for the default Hebrew LangSys, but NOT for the IWR (Hebrew/Israel) language system. When browsers render Hebrew text with lang=“he”, they activate the IWR language system, which only has the mark feature registered. Since kern is missing from IWR, browsers skip kerning entirely.
Impact:
Hebrew kerning doesn’t work at all in web browsers (Chrome, Safari, Firefox) even though the kerning data is correctly compiled into the font. This affects all Hebrew fonts with RTL kerning exported from Glyphs 3.
Steps to reproduce:
- Create Hebrew kerning in RTL mode (using the RTL button)
- Export to WOFF2
- Use the font on a website with lang=“he” attribute
- Kerning will not be applied
Expected behavior:
Hebrew kerning should work in web browsers just like Latin kerning does.
Glyphs version: [Your Glyphs 3 version number]
Let me know if you need any font files or additional information to reproduce this!