Shows a tree view of the GNML file. Whenever you select a panel (panel), a balloon (balloon), a caption (caption), a character (gl:character), a subpanel (gl:subpanel), a diegetic text (gl:diegeticText), an object (gl:object) or onomatopoeia (gl:onomatopoeia) the corresponding poylgon will be selected in the editor and highlighted in the hierarchy.