Describes any default value that the function parameter has.
See ISO/IEC 14882:2003(E) 8.3.5 Functions [dcl.fct] and 8.3.6 Default arguments [dcl.fct.default]
cxxFunctionParameter
apiRelation,
topic/ph reference/ph apiRef/apiData apiOperation/apiData cxxFunction/cxxFunctionParameterDefaultValue