Some modules allow prepending field names with - signs for a shell switch feel thingy.
It doesn't really do anything, except pass "-foo" instead of "Foo".

What you're interested in is how the module constructor takes care of the key/value pairs.

I snooped a bit in Tk, but since I've never used it (MacOS Classic here) I've only to tell you that it hashes it's arguments. Take it as if you're assigning to hash.
I know Net::Telnet treats -foo and Foo as synonyms, so I'm assuming Tk doesn't fuss over it either.

In short - Perl or perl don't make any special meaning for them...

-nuffin
zz zZ Z Z #!perl