Why are some files missing from `package.Syntax`?

[chrismwendt]

For some reason, some identifiers are present in pkg.TypesInfo, but their position does not appear in pkg.Syntax. Example: https://github.com/yuin/gopher-lua/blob/master/parse/parser.go

Maybe it has something to do with yacc and generated files?

Reported in Slack, introduced in #199, fixed in #210

cc @tjdevries