-mstrict does nothing useful, just like 'require strict;'.
Thanks, fixed.
Although I maybe it's more like 'use strict ();'

$ perl -mstrict=vars -le 'print $x**$y;'
Global symbol "$x" requires explicit package...
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perlrun says "Any meaningful switches on that line will be applied" but "meaningful" seems to be strangely implemented. At least with 5.6.1.

Here's another one:

$ perl -x
#!perl -wl -Mstrict -MB -MCGI
Argument "MCGI" isn't numeric in subtraction (-).
Argument "-MB" isn't numeric in subtraction (-).
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