  We discuss structural similarities between Knizhnik--Zamolodchikov equations
(in fact, their simplest version needed to introduce the Drinfeld associator)
and Dyson--Schwinger equations. We emphasize that the latter allow for a
filtration by co-radical degree using quasi-shuffle products and the lower
central series filtration of the Lie algebra of Feynman graphs. This clarifies
how they are a generalization of the KZ equations. This is a starting point for
a algebraic organization of the next-to...-to leading log expansion which has
been worked out in collaboration with Olaf Krueger and which will be given
elsewhere [1,2].
