Door gap above bathroom

[Kaufnizer]

It's this gap above the bathroom door designed to let warm air in? Or is this an oversight during my build?

Seems like it has to have a purpose. Only thing I can think of is letting warm air in.

[gbaglo]

To allow air circulation, which prevents mould.
Some people have put vents in the bench seats etc. for the same purpose.

[cpaharley2008]

Early doors did not allow air circulation and we had to cut holes in the door. Now there is air both up and below for circulation.