However, there is a backport of the fragment system available in the Android
Support package. This works back to API Level 4, so if your minSdkVersion is lower
than 11 and you want to use fragments, the backport is something that you will wish
to consider. You will need to add the support-v4 JAR to your project (e.g., via
compile 'com.android.support:support-v4:...' in your dependencies in
build.gradle, for some value of ...). You will also need to use
android.support.v4.app.Fragment instead of android.app.Fragment.