[wsia][wsia-requirements][R413]

R413 [Expressiveness]
		Producer properties should allow for the specification of
validation constraints and/or logic at each of the following levels: 
1.	lexical
2.	syntactic
3.	semantic
4.	Constraints linking two property elements, defining how the value of
one may be computed from that of the other. Debate: CW, SR, AK, SF, SA. Also
414-415

	Reword #4:  

	By reference to the value(s) of one or more properties already
defined.