TypeAssertion ::= Expression “as” TypeStuff
    TypeStuff ::= TypeStuffItem+
    TypeStuffItem ::= Block | any     token except , ; ) } ]
    Block ::= ParenBlock | CurlyBracketsBlock | SquareBracketsBlock | AngleBracketsBlock
    ParenBlock ::= ( ParenBlockItem* )
    ParenBlockItem ::= Block | any token except ( )