The XMLNS parser uses this field type for syntax elements that represent an XML attribute.
The name and value of the syntax element correspond to the name and value of the XML attribute that is represented. Attribute elements have no children and must always be children of an element.
When the XMLNS parser generates a bit stream from a message tree, occurrences of ampersand (&), less than (<), greater than (>), double quotation mark ("), and apostrophe ('), within the attribute value, are replaced by the predefined XML entities &, <, >, ", and '.
The XML.attr field type constant is also supported for compatibility with earlier versions.