Defining own globals

Hello, Would it be possible to make all hard-coded variables beginning with $_ automatically global? I've found useful to set some variables per page to $_PAGE variable (for example $_PAGE['title'] etc) that would be nice to get available to all functions without extra procedures (like global command). The best way could be that $_ variables can't be defined by any user-input (forms, cookies etc)... Well, that's a explanation. I hope that someone would give any hint concerning this subject. :) Best regards, Ville