A special attribute named xml:space MAY be attached to an element to signal an intention that in that element, white space should be preserved by applications. (values preserve/default)
The values of the attribute are language identifiers as defined by [IETF RFC 3066], Tags for the Identification of Languages, or its successor; in addition, the empty string MAY be specified.
Specify a base URI (used to resolve relative URI's) other than the base URI of the document or external entity.
Instead of using the 'ID' type. This can make sure the value for this attribute is unique within the XML document
The prefix xml is by definition bound to the namespace name http://www.w3.org/XML/1998/namespace, this namespace does not have to be included in the document.