Returns slice of data element if the item is deep
        indexable. Warns if attempting to slice an object that has not
        been declared deep indexable.

def _dataslice(self, data, indices):
        """
        Returns slice of data element if the item is deep
        indexable. Warns if attempting to slice an object that has not
        been declared deep indexable.
        """
        if self._deep_indexable and isinstance(data, Dimensioned) and indices:
            return data[indices]
        elif len(indices) > 0:
            self.param.warning('Cannot index into data element, extra data'
                               ' indices ignored.')
        return data