php man page for _session

_SESSION(3)								 1							       _SESSION(3)

$_SESSION - Session variables

	An associative array containing session variables available to the current script. See the Session functions documentation for more infor-
       mation on how this is used.

       $HTTP_SESSION_VARS contains the same initial information, but is not a superglobal. (Note that $HTTP_SESSION_VARS and $_SESSION are differ-
       ent variables and that PHP handles them as such)

       +--------+---------------------------------------------------+
       |Version |						    |
       |	|						    |
       |	|		     Description		    |
       |	|						    |
       +--------+---------------------------------------------------+
       | 4.1.0	|						    |
       |	|						    |
       |	|  Introduced  $_SESSION that deprecated $HTTP_SES- |
       |	| SION_VARS.					    |
       |	|						    |
       +--------+---------------------------------------------------+
       Note

	      This is a 'superglobal', or automatic global, variable. This simply means that it is available in all scopes  throughout	a  script.
	      There is no need to do global $variable; to access it within functions or methods.

       session_start(3).

PHP Documentation Group 													       _SESSION(3)