Jon, if you place code in the Placeholder body, the Page & Layer gallery shows it as HTML Placeholder.
Sadly, if it is in the Placeholder head, it states as the particular shape, typically Rectangle.

Ignoring Xara's inconsistencies, you can give each Placeholder a Name.
This means, the HTML code will show it as have an ID of that Name.
Also, the Name gallery will display the Used Names on a Page so it is easy to find one. Sadly, page by page and only for XDPX.

I occasionally, add a !Code layer and hide it. You have to name it !something so it is published even when hidden (https://www.talkgraphics.com/showthr...anced-features #2).

Finally, I sometimes create a very special Shape with a label it "CSS3-style effect" or "jQuery-action" and change that into a Placeholder so I can remember which blob is doing what.

No documentation on how Widgets are assembled but siran is the one who has done the most on this aspect.
Dig out a text editor and look at some *.xwr files in your local cache.

I need an example of what you are trying in WowSlider.

The htmlclass was a Tweak introduced after I asked for it.
It is a special Name that adds the quoted text as a number of classes.
Your example htmlclass = "hide recipient-email" (corrected the quotes) adds the class of hide and the class of recipient-email to the object's HTML.

Acorn