I am fairly sure that's not the source that produces the interaction. Apart from the incorrect expression, the mismatched brackets in (sin(x)} indicate that.
Yes, I noted the mismatch too. So what is producing the interaction then (and how does it know what changes with the interaction). It must have something to do with "user" in "userline", that is, "userline" is some primitive that includes interactions. How exactly, I cannot find.