[PPC0021] - more clarification for the short circuit behavior

Given the following code

@{ $possibly_undef?->[0] }[0..10]

What should happen if $possibly_undef is undef? had it been a chain, then it's obvious that the final slice operation would be skipped. Do we want this behavior also in the event that an equivalent expression has been made that just so happens to not be in a "chain"?

I vote yes, b/c the logic for skipping deeper parts of the chain (ostensibly) is "given that i'm trying to fetch some value deep inside this thingy, all fetching of values will be obviously undef, so let's just return undef now". That would apply to this use case also.

I'll happily submit a PR including this as a more peculiar case once i get the feeling that this I am correct that this behavior is correct

Start with the Perl expression in the issue and compare its proposed behavior with the short-circuit behavior of an equivalent chain. Resolve whether the final slice is skipped when $possibly_undef is undef, then document the agreed semantics clearly in the PPC proposal. No implementation file or test is named, so the scope must be established before coding.