We show how confluence criteria based on decreasing diagrams are generalized
to ones composable with other criteria. For demonstration of the method, the
confluence criteria of orthogonality, rule labeling, and critical pair systems
for term rewriting are recast into composable forms. We also show how such a
criterion can be used for a reduction method that removes rewrite rules
unnecessary for confluence analysis. In addition to them, we prove that
Toyama's parallel closedness result based on parallel critical pairs subsumes
his almost parallel closedness theorem.