diff --git a/format/seat-definition.schema.json b/format/seat-definition.schema.json
index 1b0888b..7ca51ea 100644
--- a/format/seat-definition.schema.json
+++ b/format/seat-definition.schema.json
@@ -354,7 +354,7 @@
             "act",
             "warrant"
           ],
-          "description": "read: invokers, persons and sessions; act: operator and sessions; warrant: operator alone, with needs-approval (design 47 G 391). A verb without it on main is a read; a verb added in design 47 G names it"
+          "description": "read: invokers, persons and sessions; act: operator and sessions; warrant: operator alone, with needs-approval (design 47 G 391). A verb that names no class is a read, whether it is on main or design 47 G adds it, and nothing refuses a verb for naming none (design 47 G 456)"
         },
         "needs-approval": {
           "type": "boolean",
@@ -373,6 +373,13 @@
           "type": "string",
           "pattern": "^[a-z][a-z0-9-]*$"
         },
+        "stream": {
+          "enum": [
+            "check",
+            "delivery"
+          ],
+          "description": "the stream an accepted kind rides: its subject is <stream>.<kind>, and one kind name may ride both streams, as the build seats accept step on check and on delivery (design 47 G 455)"
+        },
         "body": {
           "type": "object",
           "description": "a JSON Schema"