Question mark (?) in XML attributes for Android

Question

Can anyone explain the question mark means in Android XML attributes?

<TextView    
    style="?android:attr/windowTitleStyle"
    More attributes
/>

Answer 1

The question mark means it's a reference to a resource value in the currently applied theme. See the linuxtopia Android Dev Guide or the android.com Dev Guide for more about it.

? escapes the question mark.