ed n non-overlapping spans in the containing offset range.
        This will divide the contained spans as evenly as possible in the containing span,
        but if there are too many some will get squeezed all into the same last length-1 span.
        The containing span must be at least of length 1.

        Args:
            start: start offset of the containing span
            end: end offset of the containing span
            n: number of spans to embed

        Returns:
            list if embedded S