code: function( evaluator, guard, boundary ) {
  			var walkerRange = this.clone();
  			walkerRange.collapse();
  			walkerRange.setEndAt( boundary || this.root, CKEDITOR.POSITION_BEFORE_END );
  
  			var walker = new CKEDITOR.dom.walker( walkerRange );
  			walker.evaluator = evaluator;
  			walker.guard = guard;
  			return walker.next();
  		}
docs: Traverse with {@link CKEDITOR.dom.walker} to retrieve the next element before the range start.
  
  @param {Function} evaluator Function used as the walker's evaluator.
  @param {Function} [guard] Function used as the walker's guard.
  @param {CKEDITOR.dom.element} [boundary] A range ancestor element in which the traversal is limited,
  default to the root editable if not defined.
  @returns {CKEDITOR.dom.element/null} The returned node from the traversal.