Hi,

generating and displaying the elements #bbcode-options, #ajax-preview and #image-canvas (I don't know the purpose of the latter two elements)

The first (#ajax-preview) is used to show the posting by clicking at the -icon. The second one (#image-canvas) is used, when you enlarge an image, eg.g [img=thumbnail].

Is it possible to add theme-dependent JS-code without interaction with the main.js?

You can add another JavaScript file. To avoid conflicts, choose unique class-names.

Ah, „manual“ namespaces.

No, that's not the right description. I believe, the JavaScript is robust and you can add your own code. Just avoid object names that are still in use like Posting (e.g. new Posting(<id>).

/Micha