variable name characters allowed.

[webmasterpdx]

Is there a way to know what characters can be used in a variable name and also as the first character in the name. e.g. V_1 is a valid variable name, but _V1 is not. Also, there are "other" characters from the Char key that are allowed, but I don't know how to tell which ones are valid. e.g. %1 is valid, but $1 is not. Likewise some of the odder characters like the w omega character is valid, and others are not. I test them by trying them out.
Anyway, if anyone knows whats valid in the name and also what is valid for the first character...please let me know.

Note that while I can use regular alpha chars, I was thinking there might be uses in obfuscation for those who want to protect their program code.