A Range represents the list of discrete items between some starting (or from) value and working up towards some ending (or to) value. For a reverse range, the list is obtained by starting at the to value and working down towards the from value. The concept of working up and working down is dependent on the range implementation. In the general case, working up involves successive calls to the first item's next() method while working down involves calling the previous() method. Optimized numerical ranges may apply numeric addition or subtraction of some numerical step size. Particular range implementations may also support the notion of inclusivity and exclusivity with respect to the ending value in the range. E.g. 1..3 == [1, 2, 3]; but 1..<3 == [1, 2]. In general, the second boundary may not be contained in the range, and a..b may produce a different set of elements than (b..a).reversed(). E.g. 1..2.5 == [1, 2]; but 2.5..1 == [2.5, 1.5]. Implementations can be memory efficient by storing just the from and to boundary values rather than eagerly creating all discrete items in the conceptual list. The actual discrete items can be lazily calculated on an as needed basis (e.g. when calling methods from the java.util.List interface or the additional step methods in the Range interface). In addition to the methods related to a Range's "discrete items" abstraction, there is a method, containsWithinBounds which, for numerical ranges, allows checking within the continuous interval between the Range's boundary values.