I get it now. The values for the p3 and p4 properties are invalid JSON. I think of the () around values as enabling us to embed ObjectScript inside JSON.

set myObject = { "p1":"abcd", "p2":true, "p3":(value), "p4":(sum+2) }
<- ObjScript -><-------------------- JSON----><ISOS-><-JSON><-ISOS><JSON>

What do you mean by "the last two properties (p3, p4) are invalid JSON properties"? If you set the referenced variables, and add the required parentheses, it works, right?

USER>set value = 2, sum = 3
USER>set myObject = { "p1":"abcd", "p2":true, "p3":(value), "p4":(sum+2) }
USER>zw myObject
myObject={"p1":"abcd","p2":true,"p3":2,"p4":5} ;