Which of the 450943239 Mason modules am I supposed to be looking at? I checked several, and Mason appears to be (a) something you have to install separately from the main Perl installation and (b) not even close to the format I just stated. I am not looking for a templating system - I already know of several, and for that matter could roll my own - but am rather looking for something that lets you embed Perl code inside HTML pages through simple "on Perl" / "off Perl" tags and a special page ending (settable through .htaccess, of course).
Look at the distribution name, not the module name. It's a distribution you have to install in addition to the main Perl installation. I think it's pretty similar to the kind of syntax you're talking about, no?