Note only VDAFs without aggregation-ordering requirement are supported.

draft-ietf-ppm-dap.md

@@ -584,9 +584,12 @@ Aggregators. This scheme has two important properties:
   their shares locally into "aggregate shares", which may later be combined
   into the aggregate result.
 
-Note that some VDAFs allow measurements to be aggregated multiple times,
-each time with a different aggregation parameter; however, DAP only allows each
-measurement to be aggregated once.
+Note that some VDAFs allow measurements to be aggregated multiple times, each
+time with a different aggregation parameter; however, DAP only allows each
+measurement to be aggregated once. Similarly, some VDAFs produce aggregate
+values which depend on the order in which the measurementas are aggregated;
+however, DAP only supports VDAFs whose aggregation results are independent of
+the order in which measurements are aggregated (see {{Section 4.4.1 of !VDAF}}).
 
 ## System Architecture {#system-architecture}