https://helpx.adobe.com/flash-player/release-note/fp_20_air_20_release_notes.html
Authoring for Flash Player 20
To use the new Flash Player, you will need to target SWF version 31 by passing "-swf-version=31" as an extra compiler argument to the ASC 2.0 compiler.
Authoring for AIR 20 Update to the AIR 20 namespace
You must update your application descriptor file to the 20 namespace in order to access the new AIR 20 APIs and behavior. If your application does not require the new AIR 20 APIs and behavior, you are not required to update the namespace. However, we recommend all users start using the AIR 20 namespace even if you are not yet taking advantage of the new 20 capabilities. To update the namespace, change the xmlns attribute in your application descriptor to: