Am I getting true north or magnetic north from deviceorientationabsolute:alpha / deviceorientation:webkitCompassHeading

I know there are two different APIs for getting compass heading in Javascript, one for iOS and one for everyone else, aka android:

• on iOS I request permission, then listen for deviceorientation events and snag the event.webkitCompassHeading value.
• on Android I listen for deviceorientationabsolute events and snag the event.alpha value.

I have been assuming that this value returns a bearing to magnetic north, and that for mapping purposes, I should adjust, using the geomagnetism library, to point to true north.

That said, I realized that none of the guides or spec pages that I’ve read confirm this fact… This leaves me with two questions:

• Is the deviceorientation::webkitCompassHeading value relative to magnetic north, or has it already been compensated to true north?
• Is the deviceorientationabsolute::alpha value relative to magnetic north, or has it already been compensated to true north?

I know the adjustment is likely too small to matter compared to the inaccuracy of the compass itself (at least for most populated areas), but I wanted to know for sure.