This is the same reason that CGI.pm offers Tr() and TR() in place of tr() for the table row HTML element -- tr is an operator that can't be overloaded. Same with the s HTML tag (for striking through text). And if they ever come out with a y or m tag, they'll have to be called as Y() and M().

$_="goto+F.print+chop;\n=yhpaj";F1:eval