def _split_label(self, label: str) -> Tuple[str, Optional[str]]:
        """Split Entity label into ent_label and ent_id if it contains self.ent_id_sep

        label (str): The value of label in a pattern entry
        RETURNS (tuple): ent_label, ent_id
        """
        if self.ent_id_sep in label:
            ent_label, ent_id = label.rsplit(self.ent_id_sep, 1)
        else:
            ent_label = label
            ent_id = None  # type: ignore
        return ent_label, ent_id
Split Entity label into ent_label and ent_id if it contains self.ent_id_sep

        label (str): The value of label in a pattern entry
        RETURNS (tuple): ent_label, ent_id
        
spacy/pipeline/entityruler.py