OK, it is not a showstopper or critical but it is not so nice that the first example of XML syntax in the officiale XML documentation guide is not well formed: the <guide> tag is not matched by any </guide> tag :)
Like the title for example 2.1 say: "The initial part of a guide XML document". So this is just a part from the document, not the whole guide. After that chapters and sections follow. That's why there is no </guide>. Also the lines after the example say: "Following it, there's a <guide> tag -- the entire guide document is enclosed within a <guide> </guide> pair."