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_PAR. 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.