espace decla- ration to indicate the namespace on which the presence document is based. The <tuple> element: The <tuple> element carries a PRESENCE TUPLE, consisting of a mandatory <status> element, followed by any number of OPTIONAL extension elements, followed by an OPTIONAL <contact> ele- ment, followed by any number of OPTIONAL <note> elements, followed by an OPTIONAL <timestamp> element. The <status> element: The <status> element contains one OPTIONAL <basic> element that contains one of the following strings: "open" or "closed." The values "open" and "closed" indicate availability to receive the message. The <contact> element: The <contact> element contains a URL of the contact address. It optionally has a 'priority' attribute, whose value means a relative priority of this contact address over the others. The <note> element: The <note> element contains a string value, which is usually used for a human readable comment. The <timestamp> element: The <timestamp> element contains a string indicating the date and time of the status change of this tuple. 3.2.3 Status Value Extensibility: the existing PIDF definition allows arbi- trary elements to appear in the <status> element. The following example XML Schema defines an extension for <location> presence information, which can have the values of 'home,' 'office,' or 'car.' 5.4.3 Examples Simple example: <?xml version="1.0" encoding="UTF-8"?> <presence emlns="urn:ietf:params:xml:ns:pidf entity="presi ::somebody@handbook.com"> <tuple id="dsfrl3"> <status> <basic>open</basic> </status> C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security <contact priority="0.5">tel:8145557777 </contact> </tuple> </presence> Example with Status Extensions <?xml version="1.0" encoding="UTF-8"?> <presence emlns="urn:ietf:params:xml:ns:pidf" ins:im="urn:ietf:params:xml:ns:pidf:im alns:myex="http://id.hamdbook.com/ entity="pres:somebody@handbook.com"> <tuple id="dstw234"> <status> <basic>open</basic> <im:im>idle</im:im> <myex:location>car</myex:locatio