XST is a prefix that can append to function names where these functions have several streaming formats.

E.g.

function shn_XST_rms_req_new()
{
    include_once ('handler_req_new.inc');
}

Above function needs default HTML stream and Text stream where HTML stream for default behavior and Text stream for AJAX functions. If we do not have this XST prefix developers have to write functions for each and every streaming requirements (two functions for above example). In order to avoid code duplication, developers can use XST prefix in their functions.

Developers can stream data from non module functions using this module. As you know Sahana framework needs module name to stream data. But, some functionalities like location handler does not have specific module. So that earlier these functions used xml.php to stream. In order to avoid xml.php or stream.php, develpers can use xst module.

E.g.

var url2=url + "act=get_loc&mod=xst&stream=text&lvl="+curlevel+"&sel="+selection;