UMLR — Observations in TimeExpressions

In section 8.4.4 dealing with TimeExpression and Duration (both of which are kinds of ValueSpecification) it currently says:

"A TimeExpression or Duration is denoted by the textual representation of its expr, if it has one (see sub clause 8.3.5). The representation is of a formula for computing the time or duration value, which may include the names of related Observations and constants. If a TimeExpression or Duration does not have an expr, then it is simply represented by its single associated Observation."

It is not clear to me what is meant by "which may include the names of related Observations ". An Observation in the current time model is a kind of PackageableElement and not a value specification; i.e., it does not represent a value. The above text seems to suggest some kind of special case for Observation such that it should be treated as a value when its name appears in a TimeExpression or Duration. If so, what is the type of that value and where is it stored? (Note that Observation does not have an attribute for storing such a value.) What happens if the expression is one that computes the value of the Observation? Or, if the value of the Observation is needed to compute some other value?

I suggested earlier that this problem can be easily resolved if we make Observation a kind of ValueSpecification, but this does mean a metamodel change.