This
attribute is a string which is to be used as the namespace prefix for all XML elements
created as a result of writing an AST
Object out through an
XmlChan. The URI associated
with the namespace prefix is given by the symbolic constant AST__XMLNS defined in
ast.h. A definition of the namespace prefix is included in each top-level element
produced by the XmlChan.
The default value is a blank string which causes no prefix to be used. In this case
each top-level element will set the default namespace to be the value of AST__XMLNS.