General Discussions

I am planning to create an arduino-based quadruped robot, and I am trying to grasp the concept by looking at Nybble's programs. However, I don't really understand these lines from the Nybble.ino file:

 case 0xFFA25D: PTLF(" CH-");          return (F("sit")); 

I think of the "sit" as a movement array (written on Instinct.h), but I can't find anything about the others (PTLF, F). Can somebody please explain to me about them? And how to define a new movement? Thanks