def _is_triple_quoted_string(self) -> bool:
        """Is the line a triple quoted string?"""
        if not self or self.leaves[0].type != token.STRING:
            return False
        value = self.leaves[0].value
        if value.startswith(('"""', "'''")):
            return True
        if value.startswith(("r'''", 'r"""', "R'''", 'R"""')):
            return True
        return False
Is the line a triple quoted string?
src/black/lines.py