Michael Day

I couldn't find a font that triggers an actual error, because the font that we hit just returns the wrong glyph if you don't add id_delta, but it's still a...

That is true, placing it at the beginning of the phrase ("OpenType shaping documents") makes it sound like it comes _from_ OpenType (Microsoft), perhaps placing it at the end ("Complex...

That's a good point about being from a shaping implementation point of view, as contrasted with Liang Hai's work for type designers and font developers: https://github.com/typotheque/text-shaping By the way I...

The placeholder site is up with links to the specs we have been consulting so far: https://fontspec.org

An Implementation Guide for OpenType Shaping Text Shaping in OpenType: A Detailed Specification OpenType Layout Explained

The scriptListOffset, featureListOffset, and lookupListOffset fields in the GSUB/GPOS header may be NULL, despite the spec only suggesting that featureVariationsOffset may be NULL.

A NULL offset is at least a clear indication of a missing value, although it makes more sense for values which are explicitly optional. The weird situation we've encountered with...

Yes if it points to a valid value that's fine, although a little weird, but the reason we noticed in the first place is because it wasn't valid :laughing: Something...

Another thing that would be good to clarify is the way nested contextual lookups use their own lookup flag, but other lookups within a contextual lookup use the parent's lookup...

Also GSUB lookups must be sorted by lookup index before being applied, but as I recall GPOS lookups must not?