Editing Spec.isa (section)

=== Example 2 - aarch64 ===
Also note that the field name itself is arbitrary.  We can take an excerpt from https://github.com/Stuffe/isa_spec/blob/main/spec_lib/aarch64/aarch64.isa as an example:
<pre>
condition_code
eq 0000
ne 0001
cs 0010
hs 0010
</pre>
(In this case, all 16 values are included in the ISA itself, and has been truncated here for the sake of brevity.)

We can see a couple of other features in this example:
* The field name is not <code>register</code>, as noted.
* The field is four bits wide rather than three.  In principle, the fields can be any width desired (greater than zero).