Hello Reto,

From your (very well informing and thorough!) book on p. 27, "incorporate a support library", i understood that when i inserted android-support-v4.jar in my build path, then i could support platforms with api 4 or above for classes that were introduced in api 11 for instance.
I installed via Android tools/support library after rigtht clicking the project in the package view and updated the java build path many times, but nothing helps to escape from the warnings that i use classes for API 11 and that the minimum SDK is lower.. So the only thing that helps is change the minimum in the manifest to 11.
It is only clear that for instance a class from api 11 like Notification.Builder, see chapter 10, is not covered by this support library.

After some more reading in the developers guide i found that the problem was not a bug in Eclipse but my expectation that i could just use an api 11 class like Notification.Builder with android-support-v4 to support an older platform than api 11. See page 410 in the book for instance.
So Notification.Builder is not present in the support lib, but when it is renamed to NotificationCompat.Builder, then it is recognised also with lower minimum SDK than 11
It is now apparent to me that just adding the support library to the java build path is not enough to use the same code for lower platforms. The code has also to be adapted for the classes that are involved...