1. A printer comprising: a controller for transmitting commands for representing various instructions; and an engine for executing print based on the transmitted commands, wherein the commands are classified into a plurality of layers, each of the instructions is determined by at least a first command of a superior layer and a second command of a subordinate layer of the plurality of layers, when the engine receives the first and second commands, the engine executes the instruction specified by the first and second commands, and when the engine receives the second command without receiving the first command, the engine executes the instruction specified by the first command last received and the second command now received.