How to align LinearLayout at the center of its parent?

These two attributes are commonly confused:

• android:gravity sets the gravity of the content of the View it’s
  used on.
• android:layout_gravity sets the gravity of the View or
  Layout relative to its parent.

So either put android:gravity="center" on the parent or android:layout_gravity="center" on the LinearLayout itself.

I have caught myself a number of times mixing them up and wondering why things weren’t centering properly…