An XML document is valid if it has an associated document type declaration and if the document complies with the constraints expressed in it. The document type declaration must appear before the first element in the document. Example 8 Text can be interspersed with elements. Example 9 Attributes are used to associate name-value pairs with elements.
White space consists of one or more space characters, carriage returns, line feeds, or tabs.
No element type may have more than one ID attribute specified. The value of an ID attribute must be unique between all values of all ID attributes. If an attribute is implied, a default value can be provided for the case when the attribute is not used. In such a case it can contain only attributes but no text.