Creating user-defined build settings

Select the project's Build Settings tab, as in the following screenshot (so not the target's settings):

1. Click on the + button to the right of the Level button and select Add User-Defined Setting from the contextual menu.
2. Name the new setting BUNDLE_ID_SETTING. In the User-Defined section (at the very bottom) of the Build Settings tab, you now have your new setting.
3. Make a short detour to the target's General tab, and copy the Bundle Identifier field's text:

1. Back in the project's Build Settings tab, click on the disclosure triangle to the left of the BUNDLE_ID_SETTING name, and paste in the bundle identifier you have just copied.

1. Add the suffix .dev to the bundle identifier in the Dev configuration's field, so that the three user settings look as follows:

So far, so good. The only thing we need to do now is to modify the Info.plist to adopt the new setting.