iOS: how to understand the role of rootviewcontroller and its relationship with other objects

I have created a UISplitViewController based iOS app in XCode 3.2.5

Below is a screen shot of Interface builder showing the rootviewcontroller and how it is linked to other objects.

Being a beginner myself, I do not understand:

1) What is the role of the rootviewcontroller? Searched the documentation but what I found did not answer this question.

2) I thought a IBOutlet should only link to one开发者_StackOverflow中文版 corresponding object. Why in this case the rootviewcontroller is linked to two?

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1) in this case, the rootViewController can handle communication between the separate views.

2) You are viewing the referencing objects. You can two different classes both able to send messages to the same class, in this case, the application delegate can talk to the rootViewController and the detailViewController also needs to be able to talk to it, in order to facilitate communication between the master and detail views.