  Let G be the automorphism group of a regular right-angled building X. The
"standard uniform lattice" \Gamma_0 in G is a canonical graph product of finite
groups, which acts discretely on X with quotient a chamber. We prove that the
commensurator of \Gamma_0 is dense in G. This result was also obtained by
Haglund. For our proof, we develop carefully a technique of "unfoldings" of
complexes of groups. We use unfoldings to construct a sequence of uniform
lattices \Gamma_n in G, each commensurable to \Gamma_0, and then apply the
theory of group actions on complexes of groups to the sequence \Gamma_n. As
further applications of unfoldings, we determine exactly when the group G is
nondiscrete, and we prove that G acts strongly transitively on X.
