Specify list mock semantics

GAP-0/DRAFT.md

@@ -211,6 +211,26 @@ TransformOperation(document, selectionSet) :
         remove it.
   1. Return {document}.
 
+**Lists**
+
+When `@mock` is applied to a selection which is a child of a list type, the
+client inserts the same _mock value_ in each corresponding array element in
+the repsonse.
+
+For example, this query inserts the same {"blurHash"} value for each item in
+{"menuItems"}:
+
+```graphql example
+query GetMenuItemPhotos {
+  business(id: "123") {
+    menuItems {
+      name
+      blurHash @mock(value: "L15hfK~ot5NL$_?GRjIV?vW?M{RP")
+    }
+  }
+}
+```
+
 # Mock Files
 
 :: A *mock file* is a `.json` file that maps each *mock variant id* to a
@@ -271,30 +291,12 @@ A *mock variant* object may contain **only** the following keys:
 
 #### data
 
-:: {"data"} stores the *mock value*. It may be a scalar, object, or `null`,
-depending on what in the operation is being mocked.
-
-The client inserts {"data"} directly under the {"data"} key of the operation's
-response — it must not be nested inside an additional {"data"} entry.
+:: {"data"} stores the *mock value*. It may be a scalar, object, array, or
+`null`, depending on what in the operation is being mocked.
 
-For example, when `@mock` is applied to an operation root, the *mock variant*
-should look like this:
-
-```json example
-{
-  "mock-id": {
-    "data": {
-      "business": {
-        "name": "The Great British Bakery",
-        "rating": 5.0
-      }
-    },
-    "__path__": "Query"
-  }
-}
-```
-
-Not this:
+The client merges {"data"} directly into the {"data"} field of the operation's
+response — it must not be nested inside an additional {"data"} entry in the
+_mock variant_:
 
 ```json counter-example
 {
@@ -312,6 +314,21 @@ Not this:
 }
 ```
 
+When applying `@mock` to a field that returns a list type, {"data"} contains the
+list value directly:
+
+```json example
+{
+  "menu-items": {
+    "data": [
+      { "name": "Pancakes", "price": "$8.00" },
+      { "name": "Waffles", "price": "$9.00" }
+    ],
+    "__path__": "business.menuItems"
+  }
+}
+```
+
 #### errors
 
 {"errors"} may contain an array of error objects conforming to the