Negative angle arguments are allowed. The axis identifier indicates which axis this rotation occurs around. If the axis identifier is omitted, the z axis is to be assumed, since this is certainly the most common axis to rotate about, in two dimensions. Alternately, they can be viewed as lookahead-assertion parenthetics, since the stack is generally assumed to be local to the production. MDPN compiler-compilers are not expected to support them.
T is the absolute translation operator.
R is the absolute rotation operator. It is followed by an optional axis identifier, and an orthogonal angle assumed to be measured in degrees. The SP's heading is set to this angle. See the r operator, above, for how the axis identifier functions. S is the absolute scale operator.