In order to disable everything else on the website and focus the user to what they are really doing, I came with the solution of adding a layer over everything except over the current form.
I don't really know if this is maybe a bit excessive for a Web application...
For example, in a reply form to add comments:
What do you think about it?
Should the user be always free to do what they want rather than telling them what to do? If the user start writing a reply, maybe they want to stop it and do any other action such as rate comments or edit another answer... Is this way of telling them what do do very intrusive for them? (Using accept or cancel in every action)