I know how to make the contents of a content control read-only. That's easy!

But what I want to do is go the other way - I want to protect the entire document template except for three text content controls (they are: article title, article sub title, article body. You can guess what I am doing with this template!). I want those content controls to be the only things in the document that can be edited by the user.

How can I do that?