In #264 @brauliobz says

Also, there must be a ExpressionNoStructLiteral and a ExpressionStmtExpr that other productions use, but I'm still trying to find a good way to show this without cluttering the grammar.

As a first idea I would propose that the productions used for these (e.g. ComparisonExpressionNoStructLiteral) are only in the grammar appendix, once that exists, and we just link to them with a note explaining why.