Clarify that interval computations involving open null boundaries can also make use of uncertainty, by adding the following to the Interval Operators section of Language Semantics:

Note that open null boundaries of intervals are treated as uncertainties for the purposes of interval computation. For example:

    intersect Interval[1, 10] intersect Interval[5 null)

This results in an interval that begins at 5, and ends at some value between 5 and 10. Implementations can accomplish this by normalizing open intervals to closed intervals with uncertain boundaries:

    If interval.low is null then interval.low = Uncertainty(minimumValue, interval.high)
    If interval.high is null then interval.high = Uncertainty(interval.low, maximumValue)

Add examples and test cases to validate the behavior:

These should both evaluate to true:

    define TestIntervalNull1: end of (Interval[1, 10] intersect Interval[5, null)) <= 10
    define TestIntervalNull2: end of (Interval[1, 10] intersect Interval[5, null)) >= 5

And these should both evaluate to false:

    define TestIntervalNull3: end of (Interval[1, 10] intersect Interval[5, null)) > 10
    define TestIntervalNull4: end of (Interval[1, 10] intersect Interval[5, null)) < 5

This is a technical correction on the grounds that the JavaScript reference implementation already behaves this way.