Android : What should I choose between ? and @ in styple

I want to use a style of android libraries, I think I should use @ (Case 2) because it apply to style item, and if it apply to android:layout_height, I think it should to use ?

but I saw a sample from website, it use ? (Case 1), I don't know why

The Case1.gif and Case2.gif is result of Case 1 and Case 2

Case 1

  <TextView
        android:id="@+id/dialog_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" 
        style="?android:attr/listSeparatorTextViewStyle"  
    />

Case 2

  <TextView
        android:id="@+id/dialog_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" 
        style="@android:attr/listSeparatorTextViewStyle"  
    />