Also, for those who would like to better introduce themselves or go deeper with the DOM, a couple of references for your study include:
For those who like the original specifications: Web Consortium DOM Technical Reference
For those who like to understand what they are reading: Introduction to the Document Object Model by Mike Hall at Brainjar.com
Another interesting read is Joel Spolsky article about How Microsoft Lost the API War which concludes with the punch line:
None of this bodes well for Microsoft and the profits it enjoyed thanks to its API power. The new API is HTML, and the new winners in the application development marketplace will be the people who can make HTML sing.