This may be a simple question, but I tried to use
The documentation doesn't mention android.hardware.sensor.gravity in uses-feature, but you can still use it I guess as it compiles?
You can put any string in there you want. Only the documented ones will have a useful effect.
Is the gravity sensor a part of something else that I don't about?
Not from the standpoint of
<uses-feature>. There is no hardware "gravity" sensor. What you think of as
TYPE_GRAVITY is a virtual sensor, as is
TYPE_LINEAR_ACCELERATION. Those values are generated based on other sensors, such as the accelerometer.