in reply to Re: b $var
in thread b $var

Seems to imply that you can't do that with anonymous subroutines.

subname may be a variable containing a code reference

"A variable containing a code reference" can be an anonymous subroutine. The doc bit that says "named subroutine" doesn't mean it the way you read it.

Ramblings and references
“A positive attitude may not solve all your problems, but it will annoy enough people to make it worth the effort.” Herm Albright
I haven't found a problem yet that can't be solved by a well-placed trebuchet