`CompALUOpSubset` is, ultimately, an `nmigen`
[record](https://github.com/nmigen/nmigen/blob/master/nmigen/hdl/rec.py#L89)
which contains a number of fields related to telling the pipeline stage
-*what to do*. (Hence the *Op* in the class name.) I won't disclose
+*what to do* and providing all the information it needs in order *to*
+"do". (Hence the *Op* in the class name.) I won't disclose
the fields here, because they're liable to change at any time. What is
important to know here is that this record exists for one purpose: to
ensure that when the interface to the ALU pipeline stage changes for
any reason, *all* consumers of that interface are updated consistently.
Because this is a record, its fields may be introspected. This happens
-frequently; it is usually the case that an Op-type record is passed
+frequently: it is the case that an Op-type record is passed
unchanged from stage to stage. However, `nmigen` does not seem to support
testing records for equality in formal assertions. (lkcl: it does) To
express this constraint without needing to update a pile of use-sites