r[RangeMap.last_item]
    'b'

    Sometimes it's useful to find the bounds for a RangeMap

    >>> r.bounds()
    (0, 6)

    RangeMap supports .get(key, default)

    >>> r.get(0, 'not found')
    'not found'

    >>> r.get(7, 'not found')
    'not found'

    One often wishes to define the ranges by their left-most values,
    which requires use of sort params and a key_match_comparator.

    >>> r = RangeMap({1: 'a', 4: 'b'},
    ...     sort_params=dict(reverse=True),
    ...     key_match_comparator=operator.ge)
    >>> r[1], r[2], r[3], r[4], r[5], r[6]
    ('a', 'a', 'a', 'b', 'b', 'b')

    That wasn't nearly as easy as before, so an alternate constructor
    is provided:

    >>> r = RangeMap.left({1: 'a', 4: 'b', 7: RangeMap.undefined_value})
    >>> r[1], r[2], r[3], r[4], r[5], r[6]
    ('a', 'a', 'a', 'b', 'b', 'b')

    c