[kag0]

Odd they reference optional types (note it seems to be a type-level optional rather than field-level) and use this `:optional` syntax. But I don't see a section that explicitly describes what optional is. Or how it's recommended to integrate with different languages.

I'm very happy to see the concept does crop up somewhere. It's always a shame to see IDLs that don't leave much room for languages to leverage null-safety features. Especially ones that don't make the distinction between the concept of optional and default (looking at you proto3).