I started out just wanting to clarify some of the confusing bits about BoxPane, ImageView, and ScrollPane, but ended up filling in javadoc for many places that had none. In particular, there are some style values (Color, Font, Insets) for which I don't think there's any documentation (other than the parts you can infer from a tutorial example). So I put javadoc on their decoders and used @link elements from many of the places they're used.
I only did this for the wtk package. There are numerous places in the Terra theme that could also link back to Color and Font docs.