In Table 1 on page 21, we claim that the interpretation of a Reaction identifier is:
"the rate of the reaction, but only if the reaction contains
a KineticLaw object; otherwise, referencing the reaction
identifier is an error"
However, no such similar restriction is stated for any other identifier: we don't claim that referencing a Parameter is an error if it has no value, no initial assignment, and no Rule that sets it, for example. In addition, I do not believe there is a validation rule that checks this. In general, in fact, it is perfectly fine to have a 'valid' SBML model that is underdetermined, and this includes 'not setting the kinetic law of a reaction': in that case, you'd do the same thing you do for any other element without any math defined.
I propose we change this line to simply:
"the rate of the reaction"