Support ErrorMap v2

diff --git a/docs/ErrorMap.md b/docs/ErrorMap.md

index d437841774..df945f5c52 100644

--- a/docs/ErrorMap.md

+++ b/docs/ErrorMap.md

@@ -41,8 +41,10 @@ to their extended information. The top-level format of the file is:

 * `version` is the current error map format. The error map is versioned

   in case the file format changes in the future, so that clients can request

-  a version they can understand. There is currently only one version, which is

-  `1`

+  a version they can understand. There is currently two versions, 1 and 2.

+  The difference between version one and two is that two allows for new

+  attributes specified in the `attrs` section for an error code. Clients

+  *MUST* ignore unknown attributes.

 * `revision` is the revision of the error map. The revision is incremented

   whenever a new error code is added. Clients can use this to compare error

   maps from different servers and select the map with the highest revision

@@ -62,7 +64,8 @@ to their extended information. The top-level format of the file is:

 _Attributes_ are the most important part of the error map as they convey _how_

 an error code should be handled. An error code may have more than a single

-attribute.

+attribute. As of version 2 clients *must* ignore unknown attributes and only

+deal with the attributes they understand.

 * `item-deleted`: This attribute means that the error is related to operating

   on a soft-deleted document.

@@ -107,6 +110,8 @@ attribute.

 * `dcp`: The error is related to the DCP subsystem.

+* `rate-limit`: The error is related to rate limitation for the client (version 2)

+

 * `success`: The operation was successful for those situations where the error

   code is indicating successful (i.e. subdocument operations carried out on a

   deleted document)