Count Words

Hello,

Given the following:

=========== xml source ==========
<poem>
  <hey_diddle>
        Hey diddle diddle, the cat and the fiddle,
        The cow jumped over the moon,
        The little dog laughed to see such sport,
        And the dish ran away with the spoon.
  </hey_diddle>
</poem>
=========== /xml source ==========

How do I count how many words are contained within the node <hey_diddle/>?

Karl