Lacking a better identification in the OP as to the kit name or number I went off and found an image of the Dragon PE in a review of the kit on Modelwarships.
to the best of my identification PE-1 is 5-bar railing, PE-2 is 3-bar with pads and PE-3 is 2-bar with a gutter rail. Referring to Classic Warships #24, Arleigh Burke Class Destroyers. The line drawings appear to show that the 5-bar railing is placed around the deck edge (should actually be stanchions with wire-rope). 3-Bar with pad railing is placed around the elevated superstructure decks, and the 2-bar/gutter railing is placed around the mast platforms and MK99 illuminator dish platforms. 2-bar railing may also be placed around the CIWS mount.