meaning of (salary, bonus)

I'm trying to understand the semantics of constructed sequences. The
following query is given as an example of a valid sequence in "3.3.1:
Constructing Sequences" in both the current XPath 2.0 and XQuery 1.0 working
drafts:

     (salary, bonus)

with the following commentary: "This expression contains all salary children
of the context node followed by all bonus children"

Can this expression be used outside a location path? I can see returning
this expression as a function result, but can someone provide other examples
of valid use? And in such a case, what is the meaning of "context node"?

Thanks,
Howard