Add 'extras' field to JSON messages for custom data.

2 files changed, 15 insertions, 1 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a04b26f8..3a393f1e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@
 * Removed factor and offset from diagnostic requests to minimize the number of
   fields, and since this is such an uncommon use case and one that can be
   handled by the client receiving the data. We may add them back in the future.
+* Add `extras` field to JSON messages.
 
 ## v0.3
 
diff --git a/README.md b/README.md
index 6c4e23b7..fd32e900 100644
--- a/README.md
+++ b/README.md
@@ -17,7 +17,20 @@ should support this).
 
 This document describes the JSON format and includes a high level description of
 each type and field. Each JSON message published by a VI is delimited with a
-`\0` character.
+`\0 ` character.
+
+### Extra Values
+
+Any of the following JSON objects may optionally include an `extras`
+field. The value may be any valid JSON object or array. The client libraries
+will do their best to parse this information into a generic format and pass it
+to your application. For example:
+
+    {"name": "steering_wheel_angle", "value": 45,
+        "extras": {
+            "calibrated": false
+        }
+    }
 
 ### Single Valued