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:
$var =& $GLOBALS["var"];
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That means, for example, that unsetting $var won't unset global variable.
In an object method, $this is always reference to the caller object.