XUSEPOST is a command that is used to force the server to submit 
form data using the post method

This command is present for those users who need to submit
already encoded form data

Example:
XUSEPOST
http://www.anysite.com/cgi-bin/search?data1=euhhf&data2=dffjg

The above example would send the data section (part after the ?
sign) to the server using the HTML post method.