Permissions on part of a document?

Can I have only part of a document hidden from unregistered users?

Right now I have to assign a whole document to a document group and link that document group to a web user group... but what if I want to have a number of document visible to the public and have just a div-tag or a p-tag or so hidden until you log in as a part of a specific web user group?

MemberCheck snippet would be a good place to start, I think that’ll do exactly what you want. Basically, you put your restricted content into a chunk and then use MemberCheck to only show the chunk to people in the desired groups.