 <p>:: = Scope resolution operator: <a href="http://www.php.net/manual/en/language.oop5.paamayim-nekudotayim.php" rel="nofollow noreferrer">http://www.php.net/manual/en/language.oop5.paamayim-nekudotayim.php</a></p> <p>The __-prefix is a convention surrounded by built-in magic: <a href="http://www.php.net/manual/en/userlandnaming.rules.php" rel="nofollow noreferrer">http://www.php.net/manual/en/userlandnaming.rules.php</a>, never start a function or variable with this if you can avoid it.</p> <p>The first is a token, the second a convention.</p> <p>If you really want to know most tokens, see: <a href="http://www.php.net/manual/en/tokens.php" rel="nofollow noreferrer">http://www.php.net/manual/en/tokens.php</a> If you want to know more about naming conventions, see: <a href="http://www.php.net/manual/en/userlandnaming.php" rel="nofollow noreferrer">http://www.php.net/manual/en/userlandnaming.php</a></p> <p>When starting out with PHP it would hurt to read Zend coding conventions, although it's not a must and not the only way by a long shot: <a href="http://framework.zend.com/manual/en/coding-standard.html" rel="nofollow noreferrer">http://framework.zend.com/manual/en/coding-standard.html</a></p>