If shultz is saying you have to pull the trigger PRIOR to Glock disassembly, meaning removal of the slide, then he's correct. Being pedantic, certainly. To me, since it is a required step in the disassembly process it is part of disassembling the pistol.
http://glockparts.com/Content.aspx?PAGE=Glock%20DisassemblySTEP 1
REMOVE THE MAGAZINE AND CLEAR CHAMBER. DO THIS BY LOCKING BACK THE SLIDE. BE SURE THERE IS NOT A ROUND IN THE CHAMBER BY VISUAL AND PHYSICAL INSPECTION. RELEASE THE SLIDE AND POINT THE PISTOL IN A SAFE DIRECTION. PULL THE TRIGGER. THEN GRASP THE PISTOL WITH YOUR THUMB UNDER THE SLIDE AND YOUR FINGERS OVER THE TOP OF THE REAR PART OF THE SLIDE.
PULL BACK APPROXIMATELY ¼ INCH.PULL DOWN ON THE SLIDE LOCK BY GRASPING IT ON BOTH SIDES WITH YOUR THUMB AND FINGER.
PULL DOWN ON THE SLIDE LOCK WHILE RELEASING THE SLIDE FORWARD. (IF YOU HAVE A NEW YORK TRIGGER YOU WILL NEED TO PULL THE TRIGGER AGAIN AT THIS POINT). BE CAREFUL TO NOT LET THE SLIDE FALL OFF ONTO A HARD SURFACE, AS IT COULD DAMAGE THE GUIDE RING.
STEP 2
REMOVE THE SLIDE AND TAKE THE RECOIL SPRING ASSEMBLY OUT. THEN REMOVE THE BARREL. YOU NOW HAVE THE PISTOL IN THE FIELD STRIPPED CONDITION.