bounded-floorlocal type, except the user is not expected to move outside a predetermined boundary, given by the boundsGeometry in the returned object.locallocal reference space tries to keep the origin stable relative to the environment.local-floorlocal type, except the starting position is placed in a safe location for the viewer to stand, where the value of the y axis is 0 at floor level. If that floor level isn't known, the user agent will estimate the floor level. If the estimated floor level is non-zero, the browser is expected to round it such a way as to avoid fingerprinting (likely to the nearest centimeter).unboundedviewerXRSession, both immersive and inline, though it's most useful for inline sessions. It's particularly useful when determining the distance between the viewer and an input, or when working with offset spaces. Otherwise, typically, one of the other reference space types will be used more often.