It seems to me that Kiarostami has always the impulse to follow up his movies. Once the work is done he feels some irrepressible need to come back to the place, to look at the people there, to meditate on the verisimilitude of what he has done; to compare the reality with his image; and to understand how people there feel about the way they came into picture.
Actually his movies are meditations about the extent to which cinematic art expresses reality, also meditations about how reality reacts to its cinematic representation: movies meditating on themselves.
It is natural for Kiarostami to follow up this process through a new cinematic story about the movie and the reality it tried to represent. And the process goes on: 'Where is the Friend's Home' was followed by 'And Life Goes On', which in turn was followed by 'Through the Olive Trees'. As his movies always blur fiction and documentary, I would say that to a certain extent a new work of Kiarostami is also a documentary about a previous one. Sometimes the documentary is obvious, some other times it is much more discreet, but always a new movie of Kiarostami echoes a previous one.
And so, after 'Ten' came (not immediately) '10 on Ten', which is the Mother of all Kiarostami's Documentaries: the master takes his whole world of cinema, decomposes this world in its primary components and puts each component before us. Imagine the Master of the Space teaching us about Length, about Width, about Height, and about Time!