These published namespace s prevent name conflicts and indicate who defined a term. They also will make the work of search engines easier, as tags become more meaningful. A name begins with a letter or one of a few punctuation characters, and continues with name characters, which include letters, digits, underscores, hyphens, colons, and periods. Names beginning with the string xml are reserved. An author can also specify an element's data type and format.
Authors can design their own data types and use public types.
Microsoft is working with the World Wide Web Consortium to define a set of standard types and will publish a list that anyone can freely use.