def fmt_polymorphic_type_reference(data_type, inside_namespace=None):
<EOL>return fmt_type_name(data_type, inside_namespace) + "<STR_LIT>"<EOL>
Produces a TypeScript type name for the meta-type that refers to the given
struct, which belongs to an enumerated subtypes tree. This meta-type contains the
.tag field that lets developers discriminate between subtypes.