Transform Feedback notation
I do not understand this notation:
One only uses the glDrawTransform calls when one is rendering the number of primitives that were captured in a previous transform feedback operation. So the first part of the notation is obvious: you need to have a previous feedback operation in order to draw it.
The second sentence makes no sense. As previously stated, you only use glDrawTransform to draw feedback operations. Generally speaking, if you're using glDrawTransform, you probably not also capturing the results of that into a feedback object. So you wouldn't be using glDrawTransform during a feedback operation.