How is browsers position altitude defined?

Question

Looking at the docs:

https://developer.mozilla.org/en-US/docs/Web/API/Coordinates/altitude

It says "altitude above sea level in meters". Does this mean it takes into account geoid data of some kind?

Answer 1

from the w3c specification (under 'specifications' of your link):

The altitude attribute denotes the height of the position, specified in meters above the [WGS84] ellipsoid.