2002 Explorer - what is this switch?

Go to your trusty '02 and open the hood.  Over on the outside edge of
the passenger's side of the engine compartment, between the air cleaner
and the coolant expansion tank, is a switch.  It is in a rubber
bellows/boot, and it is activated (pressed) when the hood is closed.

What is this?  I always sort of mindlessly assumed that it controlled an
under-hood light - until last night, when I noticed there is no
under-hood light.  Is it part of the anti-theft system?

Thanks

Bill