  We introduce an axiomatization of the notion of a semidirect product of
locally compact quantum groups and study properties. Our approach is slightly
different from the one introduced in the thesis of S.~Roy and, unlike the
investigations of Roy, we work within the von Neumann algebraic picture. This
allows the use of powerful techniques related to crossed products by actions of
locally compact quantum groups. In particular we show existence of a "braided
comultiplication" on the algebra spanned by slices of "braided multiplicative
unitary".
