Question

How do App Engine version numbers work? Are they only integers? Can I use floats? Can I reuse old version numbers?

Answer 1

From the manual:

http://code.google.com/appengine/docs/python/config/appconfig.html#Required_Elements

A version specifier for the
application code. App Engine retains a
copy of your application for each
version used. An administrator can
change which major version of the
application is default using
Administration Console, and can test
non-default versions before making
them default. The version specifier
can contain letters, digits, and
hyphens.

Each version of an application retains
its own copy of app.yaml. When an
application is uploaded, the version
mentioned in the app.yaml file being
uploaded is the version that gets
created or replaced by the upload.