def sequence(items=None, **keywords):
    """
    Makes sequence or sequence expression.

    ..  container:: example

        ..  container:: example

            Makes sequence:

            >>> abjad.sequence([1, 2, [3, [4]], 5])
            Sequence([1, 2, [3, [4]], 5])

        ..  container:: example expression

            Makes sequence expression:

            >>> expression = abjad.sequence()
            >>> expression([1, 2, [3, [4]], 5])
            Sequence([1, 2, [3, [4]], 5])

    ..  container:: example

        Flattens, reverses and slices sequence:

        ..  container:: example

            >>> sequence_ = abjad.sequence([1, 2, [3, [4]], 5])
            >>> sequence_
            Sequence([1, 2, [3, [4]], 5])

            >>> sequence_ = sequence_.flatten(depth=-1)
            >>> sequence_
            Sequence([1, 2, 3, 4, 5])

            >>> sequence_ = sequence_.reverse()
            >>> sequence_
            Sequence([5, 4, 3, 2, 1])

            >>> sequence_ = sequence_[-3:]
            >>> sequence_
            Sequence([3, 2, 1])

        ..  container:: example expression

            >>> expression = abjad.sequence()
            >>> expression = expression.flatten(depth=-1)
            >>> expression = expression.reverse()
            >>> expression = expression[-3:]
            >>> expression([1, 2, [3, [4]], 5])
            Sequence([3, 2, 1])

    Returns sequence when ``items`` is not none.

    Returns sequence expression when ``items`` is none.
    """
    import abjad
    if items is not None:
        return abjad.Sequence(items=items, **keywords)
    else:
        expression = abjad.Expression()
        expression = expression.sequence(**keywords)
        return expression
