Hi Sandor,
Glad to hear about the page-merging script!
We'd love to add the ability to add classes to objects. Let us know if you think of a good way to do this from InDesign. We'd love to support it.
Right now, you can add ALT tags and target them with CSS and JS.
There are several ways to add ALT text. From the help docs:
Alt text, an important component in accessibility on the web, is collected from the document in many forms. Button names from the Buttons panel are used, script labels are used (when available), and Alt text from the Object Export Options is used (when available). When textframes are rendered as images and no Alt text is provided using the options listed above, in5 will use text from the textframe as Alt text.
The following CSS would target an ALT tag of redBorder and apply a red border:
[alt=redBorder] { border: 1px solid red; }
The following jQuery would target the same object and hide it:
$("'[alt=redBorder]").hide();
Hope that helps!