def _prefer_paren_wrap_match(LL: list[Leaf]) -> Optional[int]:
        """
        Returns:
            string_idx such that @LL[string_idx] is equal to our target (i.e.
            matched) string, if this line matches the "prefer paren wrap" statement
            requirements listed in the 'Requirements' section of the StringParenWrapper
            class's docstring.
                OR
            None, otherwise.
        """
        # The line must start with a string.
        if LL[0].type != token.STRING:
            return None

        matching_nodes = [
            syms.listmaker,
            syms.dictsetmaker,
            syms.testlist_gexp,
        ]
        # If the string is an immediate child of a list/set/tuple literal...
        if (
            parent_type(LL[0]) in matching_nodes
            or parent_type(LL[0].parent) in matching_nodes
        ):
            # And the string is surrounded by commas (or is the first/last child)...
            prev_sibling = LL[0].prev_sibling
            next_sibling = LL[0].next_sibling
            if (
                not prev_sibling
                and not next_sibling
                and parent_type(LL[0]) == syms.atom
            ):
                # If it's an atom string, we need to check the parent atom's siblings.
                parent = LL[0].parent
                assert parent is not None  # For type checkers.
                prev_sibling = parent.prev_sibling
                next_sibling = parent.next_sibling
            if (not prev_sibling or prev_sibling.type == token.COMMA) and (
                not next_sibling or next_sibling.type == token.COMMA
            ):
                return 0

        return None

        Returns:
            string_idx such that @LL[string_idx] is equal to our target (i.e.
            matched) string, if this line matches the "prefer paren wrap" statement
            requirements listed in the 'Requirements' section of the StringParenWrapper
            class's docstring.
                OR
            None, otherwise.
        
src/black/trans.py