Difference between response.responseXML.getElementsByTagName(); and response.responseXML.documentEle

Hi All,

What is the difference between 

var result = response.responseXML.documentElement.getAttribute("result "); and 

var result = response.responseXML.getElementsByTagName("result");

and which situation we using this documentElement.getAttribute() and getElementsByTagName()

Please any one provide the difference.

Thanks in advance,

Vinuth