[PPC0019] - Should it be a sublex?

First interesting question: Should qt() strings be sub-lexed, or not..?

I.e. what do people feel -should- be the behaviour of a construction like

sub f { ... }

say qt(Is this { f(")") } valid syntax?);

Should it:

1. Yield a parse error similar to the ones given in the example above?
2. Parse as valid perl code yielding a similar result to:

     say 'Is this ', f(")"), ' valid syntax?';

3. Something else?

I feel that interpretation 2 might be most useful and powerful, but would be inconsistent with existing behaviour of existing operators. Interpretation 1 is certainly easier to achieve as it reüses existing parser structures, but given the whole point is to interpolate code inside the {braces} it might lead to weird annoying cases that don't work so well.

Does anyone have any good examples one way or other from other languages that have a similar construction?

(Cross-posted to https://www.nntp.perl.org/group/perl.perl5.porters/2024/01/msg267671.html)

Start with the proposed qt() examples and the alternatives described in this issue, then review the cross-posted Perl porters discussion. No files or tests are named; the work would need to establish a decision about sub-lexing and define what behavior is considered complete.