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Spotting References
Many syntax constructs in PHP are implemented via referencing mechanisms, so everything told above about reference binding also apply to these constructs. Some constructs, like passing and returning by-reference, are mentioned above. Other constructs that use references are:
When you declare variable as global $var you are in fact creating reference to a global variable. That means, this is the same as:
<?php
$var =& $GLOBALS["var"];
?>
That means, for example, that unsetting $var
won't unset global variable.