CONTENT_VAR — Extract a node from an XML file using XPath.
<CONTENT_VAR NAME="document('site.xml')//title"/>
Uses the XPath query specified in the NAME to extract content from the XML file specified by the document function. Note that the document function is relative with respect to the page_id of the enclosing page. If document is omitted, then defaults to the content file that corresponds to the page_id of the enclosing page.