code: function() {
  			// TODO: use indexOf, if available: (not in IE6)
  			if (this.parent) {
  				var i,
  					l,
  					ac = this.parent.children;
  
  				for (i = 0, l = ac.length - 1; i < l; i++) {
  					// up to length-2, so next(last) = null
  					if (ac[i] === this) {
  						return ac[i + 1];
  					}
  				}
  			}
  			return null;
  		}
docs: Return the successor node (under the same parent) or null.
  @returns {FancytreeNode | null}