OptionalalwaysAlways applicable
OptionalifAt least one waitable has a defined error
OptionalifAt least one waitable doesn't have a defined value or at least one waitable has a defined error
OptionalifAll waitables have defined values
OptionalifAt least one waitable doesn't have a defined value but no waitables have defined errors
Transformers that are used depending on the state of the waitables.
The first applicable transformer is used, evaluated in the following order:
ifLoaded,ifError,ifLoading,ifErrorOrLoading,always