encoding/json: documented that ,string applies only to string and numeric fields.
Fixes #4437.
R=golang-dev, adg
CC=golang-dev, rsc
https://golang.org/cl/7064045
diff --git a/src/pkg/encoding/json/encode.go b/src/pkg/encoding/json/encode.go
index 83d5ee8..fb57f1d 100644
--- a/src/pkg/encoding/json/encode.go
+++ b/src/pkg/encoding/json/encode.go
@@ -75,8 +75,9 @@
// Field int `json:",omitempty"`
//
// The "string" option signals that a field is stored as JSON inside a
-// JSON-encoded string. This extra level of encoding is sometimes
-// used when communicating with JavaScript programs:
+// JSON-encoded string. It applies only to fields of string, floating point,
+// or integer types. This extra level of encoding is sometimes used when
+// communicating with JavaScript programs:
//
// Int64String int64 `json:",string"`
//
