Reviews feature components missing from page editor, REST API questions

Hello,

I have enabled the Reviews feature, and was looking at the Reviews Message in the Page Editor in the Studio, and I noticed that the actual components used are not available on the left-hand side.  So if I delete out an item, such as "author", I can no longer drag and drop it back in, though editing the XML works fine, of course.

Is there a list of components available?  

Also, is there a reference for creating custom components for Reviews, as in, what tags are available?

Further, is the Reviews content available through the REST API?  I noticed I can see data in 

/restapi/vc/boards/id/@review/messages/linear but there's no way to get the associated product-id.

Thanks!