Returns 'xsd:string' or a more specific type for a <meta datatype="XYZ"...
    syntax using introspection.

def _python_instance_to_nexml_meta_datatype(v):
    """Returns 'xsd:string' or a more specific type for a <meta datatype="XYZ"...
    syntax using introspection.
    """
    if isinstance(v, bool):
        return 'xsd:boolean'
    if is_int_type(v):
        return 'xsd:int'
    if isinstance(v, float):
        return 'xsd:float'
    return 'xsd:string'