1. A method for controlling playback of a record carrier comprising user data and control data in digital form, wherein the control data enables playback control of the user data, the method comprising the acts of: defining playable items of the user data; and providing in the control data selection control data for enabling selection of the playable items of the user data, play data for reproduction of the selected user data, and variable data for operating on user and system variables; wherein the variable comprises at least one instruction, including an operation code indicating a type of operation to be performed, a condition code, a type of calculation and operands, wherein the operation is to be executed if the condition code has first second and third values and at least one of respective first, second and third conditions are met, and wherein the operation is executed unconditionally if the condition code has a fourth value so that the operation is performed by execution of the at least one instruction without jumps and with reduced number of commands, and wherein the operation is adapted to be performed in conjunction with at least one of said operands.