double underscore ' __ ' - why?

[rodp]

Lately I've noticed more and more the use of a double underscore before a class's variable name, e.g:

var $__variableName = null; 

Is there a reason for this, i.e. naming conventions ?

[logic_earth]

One actually should not use double underscores as PHP reserves alot of those for magic functions or variables.

However a single underscore usually dictates that the item is private.

http://www.php.net/manual/en/language.oop5.magic.php

Caution
PHP reserves all function names starting with __ as magical. It is recommended that you do not use function names with __ in PHP unless you want some documented magic functionality

I would expand that to everything including variables.

[baileylo]

My answer is obfuscation.
http://en.wikipedia.org/wiki/Obfuscated_code