OptionalsourceSpec: {Where the positions are read. lon/lat by default, matching the rest of this API.
The spec's style either names a registered style or carries it inline.
Set e.consumed to claim the tap, otherwise it also reaches the map.
Optionaloptions: SubscribeOptionsThe element stays registered until it is destroyed.
Lets many elements share ONE style object, which matters once there are thousands.
Markers and popups; elements and styles are specs. The layer and source are created on first use, released with the map.