XML : XML format when add closing tag

  <?xml version="1.0" encoding="utf-8"?>    <Result/>          

  <?xml version="1.0" encoding="utf-8"?>    <Result> abc </Result>    

if the Result node have no value it will like the first xml.

if the Result node have value it will like the second xml.

and my question is this:" is this the standard rule that if the node result have value it will add closing tag else it will not add。