  In this article, we generalise Haglund and Wise's theory of special cube
complexes to groups acting on quasi-median graphs. More precisely, we define
special actions on quasi-median graphs, and we show that a group which acts
specially on a quasi-median graph with finitely many orbits of vertices must
embed as a virtual retract into a graph product of finite extensions of
clique-stabilisers. In the second part of the article, we apply the theory to
fundamental groups of some graphs of groups called right-angled graphs of
groups.
