Well, maybe that's an argument against the entire Perl 5 language. One should also understand that the "special globality" of the special variables is going away in Perl 6, so something like %_ is going to become lexically scoped rather than globally scoped. So the p5-to-p6 translator is going to have to turn any Perl 6 use of %_ into something like %*_ to make sure the name stays global. Or if we're spiteful enough, it'll turn into %*_P5_EMULATED_GLOBAL_UNDERSCORE_PLEASE_AVOID_ or some such... :-)

Similar considerations apply to many of the other special variables that need to be rehung on filehandle objects or lexical scopes. And some of the special variables are simply going away, and will have to be emulated by the translator some other way.

So when people are tempted to rely on idiosyncracies of the Perl 5 implementation, I would remind them of this comment of Henry Spencer's from regexp.h:

   regnode program[1];     /* Unwarranted chumminess with compiler. */
[download]