File dialect as one of model.DIALECT_* constants

def dialect(self):
        """File dialect as one of model.DIALECT_* constants
        """
        if self._dialect is None:
            self._dialect = model.DIALECT_DEFAULT
            if self.header:
                source = self.header.sub_tag("SOUR")
                if source:
                    if source.value == "MYHERITAGE":
                        self._dialect = model.DIALECT_MYHERITAGE
                    elif source.value == "ALTREE":
                        self._dialect = model.DIALECT_ALTREE
                    elif source.value == "ANCESTRIS":
                        self._dialect = model.DIALECT_ANCESTRIS
        return self._dialect