That’s exactly the point: there’s a call to pos, but it invokes pos, not your sub pos. That call to pos is ambiguous to the reader.

That argument I can accept (if not agree with), but I didn't get that from the post before the update :-)

Personally I don't find it an ambiguous read. I'm pretty religious about not using () for keywords, and not using prototypes for functions so the fact that it's pos $foo rather than pos( $foo ) is already telling me that it's a keyword not a subroutine call. Combine that with knowing how perl treats clashes between subroutines and keywords and I know that it's not going to cause problems.

However I can see that it's an issue that reasonable people can differ over.