Nested Quasis

[Waldemar Horwat]

OK.  This introduces yet another lexing context, in which all productions *except* QuasiMiddle and QuasiEnd are disallowed, and white space and comment handling is funny.  That works if the expressions must be one of the two forms:

$id
${expr}

Is that the exhaustive list, or are we looking at other forms such as $$, $id.id, $id[expr], etc.?

     Waldemar