Type /test. This will echo the currently executing script plus "ing" (eg: c:\mirc\script1.mrcing). The helpfile fails to mention you can add text directly onto the end of $script like you can with $N parameters.

Seems to be this is just a parse 'glitch' and not really a feature..

It is a feature.

Other identifiers it works with include $mircdir, $logdir and $getdir (you'll notice a pattern).

It's not a feature, it's legacy stuff. See versions.txt, mIRC 5.7, point 100.

As such, it's logical that it's not documented..