Since you do not specify which SDK you are using there could only be two scenarious for it missing from the documentation:
- you are using SDKs older than S60 2nd Edition FP3 and those SDKs don't know about the flag since it was not defined at the time
- you are using an SDK more recent than S60 3rd Edition which do not document the flag because is is added by default to the application, the developers don't have to use it explicitely.