Android

Gravity and layout_gravity on Android
- android:gravity sets the gravity of the content of the View its used on.
- android:layout_gravity sets the gravity of the View or Layout in its parent.
http://stackoverflow.com/questions/3482742/gravity-and-layout-gravity-on-android

Align views at the bottom of the screen
android:layout_alignParentBottom with RelativeLayout
android:layout_centerHorizontal="true"
http://stackoverflow.com/questions/2386866/how-to-align-views-at-the-bottom-of-the-screen

Responsive Design
Since these files have large and sw600dp selectors, they are applied to tablets and TVs regardless of Android version (pre-3.2 tablets and TVs match large, and post-3.2 will match sw600dp).
width dp. For example, -w600p
height dp. For example, -h600dp
smallest width dp*. For example, -sw600dp
http://developer.android.com/training/multiscreen/screensizes.html
http://documents.mx/technology/responsive-mobile-design.html