The developer guide mentions:
"An app extension needs a short, recognizable name that includes the name of the containing app, using the pattern 'Containing app name'—'App extension name'. This makes it easier for users to manage extensions throughout the system. You can, optionally, use the containing app’s name as-is for your extension, in the common case that your containing app provides exactly one extension."
How do you make the extension show up as just 'Containing app name'? The guidelines don't really explain how to do this, just that it's possibly.
I couldn't just change the Bundle Display Name for the extension to an empty string "".
Make the extension's name match the containing app's name and the extension portion will disappear when displayed.