protected PaperOnboardingPage toggleToPreviousElement(){
  if (mActiveElementIndex - 1 >= 0) {
    mActiveElementIndex--;
    return mElements.size() > mActiveElementIndex ? mElements.get(mActiveElementIndex) : null;
  }
 else   return null;
}

protected PaperOnboardingPage toggleToPreviousElement ( ) { if ( mActiveElementIndex - 1 >= 0 ) { mActiveElementIndex -- ; return mElements . size ( ) > mActiveElementIndex ? mElements . get ( mActiveElementIndex ) : null ; } else return null ; }
changes active element to the previous one and returns a new content
