def _register_function(
        self,
        fn: Callable,
        name: Optional[str] = None,
        override: bool = False,
        metadata: Optional[Dict[str, Any]] = None,
    ):
        """Register in the first available registry."""
        for registry in self.registries:
            if getattr(registry, "_register_function", None) is not None:
                return registry._register_function(fn, name=name, override=override, metadata=metadata)
        return None
Register in the first available registry.
src/flash/core/registry.py