Complicated interpolation can be lexed as a regular language if you treat strings as three separate lexical things, eg in JavaScript template literals there are

Complicated interpolation can be lexed as a regular language if you treat strings as three separate lexical things, eg in JavaScript template literals there are, `stuff${ }stuff${ }stuff` so the ${ and } are extra closing and opening string delimiters, leaving the nesting to be handled by the parser. You need a lexer hack so that the lexer does not treat } as the start of a string literal, except when the parser is inside an interpolation but all nested {} have been closed.