xpath find if node exists

Question

Using a xpath query how do you find if a node (tag) exists at all?

For example if I needed to make sure a website page has the correct basic structure like /html/bod

Answer 1

A variation when using xpath in Java using count():

int numberofbodies = Integer.parseInt((String) xPath.evaluate("count(/html/body)", doc));
if( numberofbodies==0) {
    // body node missing
}