Right after this paragraph I would like to see an explained example of the "retrieve declaration". Otherwise I get quite confused when I see example statements like:

[Condition: severity in "Acute Severity"]

which are the retrieve expressions but are not retrieve declarations. I.e. they can not be used in the specifications by themselves and must be a part of a complete declaration like the following:

context Patient
define "Some declaration name":
[Condition: severity in "Acute Severity"]

Existing Wording:

The retrieve declaration is the central construct for accessing clinical information within CQL. The result of a retrieve is always a list of some type of clinical data, based on the type described by the retrieve and the context (such as Patient, Practitioner, or Unfiltered) in which the retrieve is evaluated.