On Birta, a draft is a project's working copy. An agent creates one, empty or copied from an already-published version, and writes its files into it one at a time. Nothing in a draft is live: the project's public address keeps serving whatever was last published, untouched, no matter how many times the draft changes underneath it.
That separation is what makes iteration safe. You can look at a draft at its own address, leave remarks on the page, and ask for changes round after round, and a visitor to the real site never sees any of it until you say the draft is good and it gets published by number.
A published draft becomes a version; the two are the same thing at different points in the loop.