  We give properties of the real-split retraction of the mixed weak
Mumford-Tate domain and prove the Ax-Schanuel property of period mappings
arising from variations of mixed Hodge structures. An ingredient in the proof
is the definability of the liftings of mixed period mappings obtained by
Bakker-Brunebarbe-Klingler-Tsimerman. In the point counting step, we count
rational points on definable quotients.
