def isel(
        self, indexers: Mapping[Any, int | slice | np.ndarray | Variable]
    ) -> Index | None:
        """Maybe returns a new index from the current index itself indexed by
        positional indexers.

        This method should be re-implemented in subclasses of Index if the
        wrapped index structure supports indexing operations. For example,
        indexing a ``pandas.Index`` is pretty straightforward as it behaves very
        much like an array. By contrast, it may be harder doing so for a
        structure like a kd-tree that differs much from a simple array.

        If not re-implemented in subclasses of Index, this method returns
        ``None``, i.e., calling :py:meth:`Dataset.isel` will either drop the
        index in the resulting dataset or pass it unchanged if its corresponding
        coordinate(s) are not indexed.

        Parameters
        ----------
        indexers : dict
            A dictionary of positional indexers as passed from
            :py:meth:`Dataset.isel` and where the entries have been filtered
            for the current index.

        Returns
        -------
        maybe_index : Index
            A new Index object or ``None``.
        """
        return None
Maybe returns a new index from the current index itself indexed by
        positional indexers.

        This method should be re-implemented in subclasses of Index if the
        wrapped index structure supports indexing operations. For example,
        indexing a ``pandas.Index`` is pretty straightforward as it behaves very
        much like an array. By contrast, it may be harder doing so for a
        structure like a kd-tree that differs much from a simple array.

        If not re-implemented in subclasses of Index, this method returns
        ``None``, i.e., calling :py:meth:`Dataset.isel` will either drop the
        index in the resulting dataset or pass it unchanged if its corresponding
        coordinate(s) are not indexed.

        Parameters
        ----------
        indexers : dict
            A dictionary of positional indexers as passed from
            :py:meth:`Dataset.isel` and where the entries have been filtered
            for the current index.

        Returns
        -------
        maybe_index : Index
            A new Index object or ``None``.
        
xarray/core/indexes.py