Global nix_get_typename (nix_c_context *context, const Value *value): way to free the result
Global NixCExternalValueDesc::printValueAsXML )(void *self, State *, int strict, int location, void *doc, nix_string_context *c, void *drvsSeen, int pos): The mechanisms for this call are incomplete. There are no C bindings to work with XML, pathsets and positions.