Ability to add 'door' markers?

[originalfoo]

I notice many workshop buildings, and even some vanilla, are missing door markers which result in cims enter/exit building through walls at the side etc.

Would it be possible to add/alter door markers with Building Spawn Points tool? It would be particularly useful if there was the usual highlighting of what they connect to when hovered.

There are three types that I am aware of:

• Door Marker
• Enter Only Door Marker
• Exit Only Door Marker