code: function(){
      if (!this.lastMousePos.pageX) return;
  
      this.selection.selecting = true;
  
      if (this.multitouches) {
        this.selection.setSelectionPos(this.selection.selection.first,  this.getEventPosition(this.multitouches[0]));
        this.selection.setSelectionPos(this.selection.selection.second,  this.getEventPosition(this.multitouches[1]));
      } else
      if (this.options.selection.pinchOnly) {
        return;
      } else {
        this.selection.setSelectionPos(this.selection.selection.second, this.lastMousePos);
      }
  
      this.selection.clearSelection();
      
      if(this.selection.selectionIsSane()) {
        this.selection.drawSelection();
      }
    }
docs: Updates (draws) the selection box.