One benefit of using this method to create the overlay is that the definition carries over from one page to another.

None of the thumbnail/popups in this article directly reference the custom overlay. All the definition was done in in the Highslide configuration.

You can restrict which thumbnail/popups qualify for the custom overlay by specifying either a Thumbnail id or Slideshow group in the custom overlay settings. For example, a thumbnail id of 'thumb4' in the custom overlay settings would restrict the overlay to thumbnail/popups with a thumbnail Id equal to 'thumb4' in the Id field of the Thumbnail tab in the HsExpander plugin.

Likewise, a slideshow group of 'group1' in the custom overlay settings would restrict the overlay to thumbnail/popups with a slideshow group equal to 'group1' in slideshow group field of the Popup tab of the HsExpander plugin.

Finally, the use of a custom overlay does not preclude you from using a custom overlay in the HsExpander or HsHtmlExpander plugins. This means that you can define a text overlay, for example, as well has having a navigation controlbar overlay.