The grating behaves a bit strangely

[eriktorbjorn]

You can lock the grating while it's open, which may be fine. But if you then try to open or close it, it will tell you that the grating is locked.

Either you should only be able to lock it when it's closed, or it should check if it's already open or closed even when it's locked. I think.

All of this is handled by GRATE-FUNCTION.