I was reading an article at
zA -> xy
is described as being an "unrestricted" production. In what way is it "unrestricted"?
I even visited https://en.wikipedia.org/wiki/Unrestricted_grammar
which talks about unrestricted grammar as the one that is comprised of productions which have no restriction on LHS or RHS. On this note, I assume that an unrestricted production is the one with no restriction on LHS or RHS.
What restrictions are being talked about and how is the production free from such restrictions?