code: function changeStep(steps, layer, bool) {
              var visibleStep = steps.filter('.is-selected'),
                  delay = (viewportSize() == 'desktop') ? 300 : 0;
              visibleStep.removeClass('is-selected');
  
              //remove class that make tour target elemment pop when selected
              jQuery(global_target_selectors[getActiveStepCount()]).removeClass('tour-target-element');
  
              (bool == 'next') && visibleStep.addClass('move-left');
  
              setTimeout(function () {
                  (bool == 'next')
                      ? showStep(visibleStep.next(), layer)
                      : showStep(visibleStep.prev(), layer);
  
                  //add class to make tour target element pop
                  jQuery(global_target_selectors[getActiveStepCount()]).addClass('tour-target-element');
  
                  //call onChange trigger if specified
                  if (jQuery.isFunction(options.onChanged))
                      options.onChanged(jQuery(global_items[getActiveStepCount()].element));//returns the current layer as JQuery object
              }, delay);
          }
docs: this changes step , if any is active call the onChanged(current_layer):JQueryObject function if specified
  @param steps
  @param layer
  @param bool