The relevant documentation from perlsyn:

       The "foreach" loop iterates over a normal list value and
       sets the variable VAR to be each element of the list in
       turn.  If the variable is preceded with the keyword "my",
       then it is lexically scoped, and is therefore visible only
       within the loop.  Otherwise, the variable is implicitly
       local to the loop and regains its former value upon exit-
       ing the loop.  If the variable was previously declared
       with "my", it uses that variable instead of the global
       one, but it's still localized to the loop.
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-sauoq
"My two cents aren't worth a dime.";