Accessibility issues

By “shadowbox” I guess you mean lightbox.

Image galleries are programmed to use links rather than buttons to trigger the shadowbox to activate.

That is an erroneous premise. Semantically, a gallery needs to be a collection of images (not buttons), which are fully formed. The fact that while clicking on an image a ligthbox is launched is incidental. To that end, each image in a gallery has a full <a> element, which is complete with a title, and alt attribute, and an href attribute pointing to a full-sized URL – everything you need from an accessibility standpoint. If you disable the lightbox functionality, the gallery will still function just as designed, and you will be taken to the full image upon clicking – you cannot do this if you swap out images with buttons. So, saying that this is an “Imporper use of link” isn’t accurate.

All the lightboxes used in Photonic are developed by third-parties, and practically all of them require your clicked element to either be an image or a link (rarely do they support buttons). Sure, to skirt the scenario, I can make a link behave like a button by adding a role to it, but the fact is, each link is actually a link to a full image. And I am not even sure if that fools a checker that is looking for JavaScript bindings.

Also, from what I recall of my testing, each lightbox’s controls supports keyboard shortcuts (left arrow, right arrow and close at a minimum). Please let me know which lightbox’s controls are not keyboard-operable.