An integer specifying the version of the manifest file format your package requires. For example:
Supported values for this key are:
3: Use the Manifest V3 format and associated feature set.
2: Use the Manifest V2 format and associated feature set.
The current version is Manifest V3. Manifest V2 is also currently permitted, but will be phased out in the future. There will be other manifest versions in the future (V4 and beyond) but these aren't scheduled yet.