I don't understand popController(Controller controller)

I was wondering what happens when I call `popController(Controller controller)` with a controller which is not the top one. A small test app confirmed what I initially saw in the sources: _The not-top-controller gets removed, all controllers above it stay untouched and the controller directly below the not-top-controller gets activated in addition to the one which was and still is the top controller._

Can someone tell me if this is desired? What is the use case? I just don't understand it. IMHO such an API should not be exposed. But maybe I'm overseeing something.

**Some details of my test program:**

1. I pushed 6 new instances of `TextController` to the router of my `testContainer` and kept a reference to the 3rd one (IID=728) stored in `mTextController3`

Debug output of the complete controller hierarchy is now:

```
------------------------------------------------------------
[IID] C V A R D B Controller @ Container # Tag
------------------------------------------------------------
[2c6] 0 x x _ _ 0 ParentController @ myContainer
[720] 1 x x _ _ 5 + TextController @ testContainer
[846] 1 _ _ _ _ 4 TextController @ testContainer
[8cc] 1 _ _ _ _ 3 TextController @ testContainer
[728] 1 _ _ _ _ 2 TextController @ testContainer
[a45] 1 _ _ _ _ 1 TextController @ testContainer
[e36] 1 _ _ _ _ 0 TextController @ testContainer
------------------------------------------------------------
```

2. Then I called `.popController(mTextController3)`

These are the only lifecycle methods which are now called in the whole system:

```
[a45] TextController.onCreateView()
[a45] TextController.onRestoreViewState()
[a45] TextController.onAttach()
```

Debug output of the complete controller hierarchy is finally:

```
------------------------------------------------------------
[IID] C V A R D B Controller @ Container # Tag
------------------------------------------------------------
[2c6] 0 x x _ _ 0 ParentController @ myContainer
[720] 1 x x _ _ 4 + TextController @ testContainer
[846] 1 _ _ _ _ 3 TextController @ testContainer
[8cc] 1 _ _ _ _ 2 TextController @ testContainer
[a45] 1 x x _ _ 1 TextController @ testContainer
[e36] 1 _ _ _ _ 0 TextController @ testContainer
------------------------------------------------------------
```

**The views of controller 720 and a45 are now attached and visible at the same time !!!**

Legend:
```
IID = Controller.getInstanceId() // first 3 chars only
C = Controller.getArgs().size() // constructor params
V = Controller.getView() != null
A = Controller.isAttached()
R = Controller.getRetainViewMode() == RETAIN_DETACH
D = Controller.isDestroyed() / .isBeingDestroyed()
B = Index of the controller in its router's backstack
```

Start by reproducing the reported popController(mTextController3) scenario with six TextController instances and inspect the router's backstack and lifecycle handling. Compare the observed hierarchy and lifecycle callbacks with the intended behavior; done means the behavior is either corrected with a regression test or clearly documented as intentional.

Written by the indexing model from the issue text.