iOS/OSX App Group Ids, start them with "group." or "team-id."?

Question

When creating a App Group id in the Provisioning Portal (or whatever its called now), it says to "Enter a unique identifier for your App Group, starting with the string 'group'" and seems to enforce that in the entry field. Also, lots of sample code uses app group id strings like "group.com.company.blah".

However, the definitive sections I've seen to linked throughout the documentation, App Sandbox Design Guide > App Sandbox In Depth > Container Directories and File System Access > The Application Group Container Directory and Entitlements Key Rerefence > Enabling App Sandbox > Adding an App to an App Group, directly contradict this, clearly stating "must begin with your development team ID, followed by a period".

The examples given in those section are like "Z123456789.com.example.app-group" and "DG29478A379Q6483R9214.HolstFirstAppSuite" respectively. (whah, is that last one a super weird team id or what?)

So with this inconsistency, what do I do to get a App Group ID to work? Should I enter in the Provisioning Portal "group.TEAM-ID.com.example.blah"? And should I use this same string in my source code strings, or omit the "group." part to be like the many code examples? Or is the documentation wrong and the team id is never needed?

Context ... I've been trying to update an iOS cocoapod's test app so I can see extension <-> app communication in action. After updating the app ids and group id to one's in my control, and when using a group id similar to the project's original one, like "group.com.mycompany.thingie", I see containerURLForSecurityApplicationGroupIdentifier: do nothing but return nil and nothing else has fixed it.

UPDATE: (added this for clarity seeing how SO informs me that this Q is getting many hits) It turns out this stuff is more forgiving than I originally thought, as the nil result turns out to have been (mostly?) my doing. See the answer & its comment thread. I haven't checked to see if the documentation & examples are any clearer yet.

Answer 1

On https://developer.apple.com inside "Certificates, Identifiers & Profiles" when you go to the "App Groups" section and first generate your App Group, all that is required is the enforced group.com.companyname.appname

As long as com.companyname.appname matches what you have setup as the bundle identifier for your target underneath general, you should be able to then go to "Capabilities" tab, turn on "App Groups" click the refresh symbol and the group you just created in Provisioning Portal should appear there, as "group.com.companyname.appname" you'll have the option to check it off, and then will have an error with entitlements. Clicking "fix issue" should automatically resolve it.

Now if you navigate to you entitlements file you'll notice that "com.apple.security.applications-groups" will have an item and it will be set to the exact same "group.com.companyname.appname" value.

I've tested on devices and have no issues yet. This doesn't account for the inconsistency in documentation, but I can guarantee that this works.