Song Versions

Versions of the song can be created, and reverted to, later. These versions include the song file and the MIDI and .aem files opened in the tracks.
Typical applications of versions include:

Create Version

The Song menu's Create Version option pops up the Create Version dialog which lets you type a name for the version to be created. If there are modifications in the song which haven't been saved yet you can choose whether you want to include the modifications in the version or not. This can come in handy if you open a song and start tweaking the mix: if you think you're onto something good you can still create a version of the song as it was when you opened it, just in case the new mix appears to be not so good after all.

Revert to Version

The Song menu's Revert to Version item lists all available versions. Tooltips show information about the versions, like the date it was created. You can revert to a version by clicking it. If there's no version that equals the song in its current state a version equaling the current state will be created. These automatically created versions are named "Autosave Version 1" etc.

Autosave

Some versions are created automatically:

Note 1: Autosave versions aren't created until the song has been saved for the first time.

Note 2: Audio files themselves are not stored in the version files, so if you edit an audio file using a third party editor all versions using that file will be affected. You can make a copy of a file and edit the copy to avoid this.

Note 3: The versions mechanism assumes there's only one song in a folder (ie. it assumes every versions it finds in the song's folder is a version of the current song). This is likely the case with MultitrackStudio 5 or newer, but you might want to make sure this is the case with songs you created with older versions before reverting to a version.

Note 4: Some third-party demo version VST / AU plugins pop up a 'demo limitation' message window when the plugin settings are written to file. These messages will appear whenever a version is created.

Under the hood
A version file (.hdrversion file extension) is a song file which also contains the .mid and .aem track data.