Merge remote-tracking branch 'remotes/upstream/Development' into Development

Marlin/Marlin.h

@@ -180,8 +180,8 @@ void manage_inactivity(bool ignore_stepper_queue=false);
   #define disable_e3() /* nothing */
 #endif
 
-enum AxisEnum {X_AXIS=0, Y_AXIS=1, Z_AXIS=2, E_AXIS=3, X_HEAD=4, Y_HEAD=5};
-
+enum AxisEnum {X_AXIS=0, Y_AXIS=1, Z_AXIS=2, E_AXIS=3, X_HEAD=4, Y_HEAD=5}; 
+//X_HEAD and Y_HEAD is used for systems that don't have a 1:1 relationship between X_AXIS and X Head movement, like CoreXY bots.
 
 void FlushSerialRequestResend();
 void ClearToSend();