AI-generated Key Takeaways
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          The App Index API includes interfaces for representing user actions and indexable units. 
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          There are builder classes available for creating Action, Indexable, and Indexable.Metadata objects. 
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          Direct use of the play-services-appindex SDK for AppIndex and UserActions is not supported. 
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          Exceptions such as AppIndexException, AppIndexInvalidArgumentException, and AppIndexTooManyArgumentsException can be thrown by the App Index API methods. 
Interfaces
| Action | Represents an action taken by the user within the app. | 
| Indexable | Represents an indexable unit. | 
| Indexable.Metadata | Represents the metadata for an Indexable. | 
Classes
| Action.Builder | The builder for Action. | 
| AppIndex | |
| Indexable.Builder | The builder for Indexable. | 
| Indexable.Metadata.Builder | The builder for Indexable.Metadata. | 
| ThingPropertyKeys | This class contains Bundle keys for setting Indexableproperties. | 
| UserActions | 
Exceptions
| AppIndexException | Class of exceptions thrown by the App Index API. | 
| AppIndexInvalidArgumentException | The exception that is thrown if an invalid argument is provided to one of the App Index API methods. | 
| AppIndexTooManyArgumentsException | The exception that is thrown if the number of
            arguments passed to an App Index API method in a single call exceeds the allowed
            maximum of Indexable.MAX_INDEXABLES_TO_BE_UPDATED_IN_ONE_CALL. |