I have A7 commercial

In the manual I came across c_content which notes that it can only be used with, I quote:

"Works only with BSP levels and the AABB collision system."

Ok all fine there but I noticed that in the manual's collision engine description it says:

"In A7, BSP trees and the AABB collision system are only supported by the Pro Edition."

Hmm oh well. Yet I did use c_content anyway and it works with A7 Com. Have I misunderstood the manual?

No, it's the manual that was not clear. You can create BSP levels with all versions, but you can render the BSP tree only with the Pro Edition. The lower editions render them with the ABT even if it's a BSP level.