marshmallow

Hi there, I am tweaking some printer initialization gcode and noticed move commands such as "G1 X5 A13 F2400" in gcode files. I've looked high and low and cant find a description of what the "A" parameter is. Testing tells me that filament is extruded when executing the move. How might this be different than the normal "E" extrusion parameter? I did find references in CNC gcode documentation to A, B and C axes but I don't think that's applicable here. Thanks for any help you can provide. Tom