This is the maximum SDK version number that an application works on. You can use this to ensure your application is filtered out of later versions of the platform when you know you have incompatibility with them.

Must be an integer value, such as "100".

This may also be a reference to a resource (in the form "@[package:]type:name") or theme attribute (in the form "?[package:][type:]name") containing a value of this type.

[Android Documentation]