All-in-one format

I have been using 2012 for writing and 2013 for building for some time.
recently I started a new project entirely in 2013 to force myself to use the new IDE.
(Still really not liking it… especially the way it keeps replacing the thing Im working on by something else. Why have tabs if you always replace the first one???)

Anyway, the issue:
I thought that xojo_project was equivalent to the old .rbp file
I accidentally opened an old project using 2013 and saved in this format

When I make changes, I like to ‘save as…’ so that I have a string of versions around.
I can open the project dated Jun2014 and know that this is what I built in June

Now, it seems that the project has saved itself in pieces, and changes I have been making on what I thought were a safe renamed copy, have actually changed the code in older differently named projects.

The question:
What format is the ‘all in one’ format that doesn’t break other projects when you save with a new name?

.xojoproject is the version control format. What you need is the binary project