An instruction to modify one or more properties within one of the property defining data structures (CHP, PAP, TAP, SEP, or PIC). It consists of an operation code which identifies the field(s) to be changed, and an operand which gives the value that a particular field is changed to or else which is a parameter to a procedure which will change the field or fields. A prl (property modifiers stored in a list) is a sprm plus its operand.