Regular Expressions: RegEx for determining valid PHP class property names?

Question

I am using PHP's magic __set and __get methods to access a private array in a class. Use of the class can include "setting" new properties as well as using existing ones. I want to make sure the property names created or requested (i.e. $myObj->FakeProperty) are valid according to the following rules:

1. Property names must begin with either a letter or underscore [A-z_]
2. If it begins with an underscore, it must be followed by a letter
3. So long as the first two rules are met, the name may contain any of [A-z0-9_]

My current RegEx isn't doing the trick; with my test values, _12 always falls through the cracks.

Test Fields:

albert12
12Albert
_12
_Albert12
_12Albert
_____a_1

RegEx:

^(?=_*[A-z]+)[A-z0-9_]+$

Answer 1

according to docs, the following would match any valid php identifier

/^[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*$/