http://www.developer.com/xml/article.php/3081641/Well-Formed-XML-Checklist.htm
One of the main reasons to use XML is to insure that anyone can read your data. To insure that anyone can, your XML must be presented in a well formed document. Well formed means that your document follows rules which allow the data to be read by any commerial parser. Using this checklist will insure that your document follows the well formed guidelines. Insure that your document:
Well Formed XML Checklist
September 23, 2003