Android Resource

1. @
   Note here the use of the '@' prefix to introduce a resource reference --
   the text following that is the name of a resource in the form of @[package:]type/name.
   In this case we didn't need to specify the package because we are referencing a resource in our own package. To reference a system resource, you would need to write:
   
2. ?
   Note that this is very similar to a resource reference, except we are using an '?' prefix instead of '@'. When you use this markup, you are supplying the name of an attribute resource that will be looked up in the theme
   -- because the resource tool knows that an attribute resource is expected,
   you do not need to explicitly state the type (which would be ?android:attr/android:textDisabledColor).
   
3. @ ?
   Other than using this resource identifier to find the value in the theme instead of raw resources, the name syntax is identical to the '@' format: ?[namespace:]type/name with the type here being optional.
   
4. android defines (*.xml)
   frameworks\base\core\res\res\values
   attrs.xml , attrs_manifest.xml , public.xml , styles.xml , themes.xml
   
5. You can get more information from SDK documments.
   Framework Topics | User Interface | Declaring Layout ....
   
6. Reference
   
   1. android resources
      
   2. Resources and Internationalization
      
   3. android read xml
      
   4. understanding-android-themes-and-styles