diff --git a/CHANGELOG.md b/CHANGELOG.md
index 92d943e6..c4449df7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,7 +5,7 @@
 - feat(definePlugin): helper function to create plugins
 - chore(package.json): update to httpxy@0.5.3
 - fix(ipv6): preserve credentials when normalizing bracketed IPv6 target string
-- fix(ipv6): unspecified IPv6 target hostname (::)"
+- fix(ipv6): unspecified IPv6 target hostname (::)
 - fix(response-interceptor): reduce responseInterceptor buffer churn
 - fix(ws): handle multi-server upgrade subscription and safe proxy shutdown
 - feat(router): add 'res' and 'options' to router function
diff --git a/README.md b/README.md
index d3071f7d..68912ed2 100644
--- a/README.md
+++ b/README.md
@@ -239,12 +239,12 @@ router: {
 }
 
 // Custom router function (string target)
-router: function(req) {
+router: function(req, res, options) {
     return 'http://127.0.0.1:8004';
 }
 
 // Custom router function (target object)
-router: function(req) {
+router: function(req, res, options) {
     return {
         protocol: 'https:', // The : is required
         host: '127.0.0.1',
@@ -253,10 +253,12 @@ router: function(req) {
 }
 
 // Asynchronous router function which returns promise
-router: async function(req) {
+router: async function(req, res, options) {
     const url = await doSomeIO();
     return url;
 }
+
+// NOTE: `res` is undefined in WebSocket upgrade flows.
 ```
 
 ### `plugins` (Array)
@@ -498,7 +500,9 @@ createProxyMiddleware({ pathFilter: '/', target: 'http://echo.websocket.org', ws
 
 ### External WebSocket upgrade
 
-In the previous WebSocket examples, http-proxy-middleware relies on a initial http request in order to listen to the http `upgrade` event. If you need to proxy WebSockets without the initial http request, you can subscribe to the server's http `upgrade` event manually.
+In the previous WebSocket examples, http-proxy-middleware relies on an initial HTTP request in order to listen to the HTTP `upgrade` event. If you need to proxy WebSockets without the initial HTTP request, you can subscribe to the server's HTTP `upgrade` event manually.
+
+When the same middleware instance is attached to multiple servers and `ws: true` is used, each server needs its own initial HTTP request before upgrades are auto-subscribed.
 
 ```javascript
 const wsProxy = createProxyMiddleware({ target: 'ws://echo.websocket.org', changeOrigin: true });
@@ -579,6 +583,10 @@ Ways to solve it:
 - Change the target server to (also) accept IPv6 connections.
 - Add this flag when running `node`: `node index.js --dns-result-order=ipv4first`. (Not recommended.)
 
+Additional IPv6 notes:
+
+- Unspecified IPv6 host `http://[::]:port` is normalized to loopback (`::1`) to reach local listeners.
+
 > Note: There’s a thing called [Happy Eyeballs](https://en.wikipedia.org/wiki/Happy_Eyeballs) which means connecting to both IPv4 and IPv6 in parallel, which Node.js doesn’t have, but explains why for example `curl` can connect.
 
 ## Debugging
diff --git a/recipes/router.md b/recipes/router.md
index 446e03be..7bf7efe8 100644
--- a/recipes/router.md
+++ b/recipes/router.md
@@ -10,12 +10,18 @@ Allows you to route to a different `target` by using a table of a custom functio
 
 Write your own router to dynamically route to a different `target`.
 The `req` object is provided to retrieve contextual data.
+The `res` and `options` arguments are also provided.
 
 ```javascript
 import express from 'express';
 import { createProxyMiddleware } from 'http-proxy-middleware';
 
-const customRouter = function (req) {
+const customRouter = function (req, res, options) {
+  options.headers = {
+    ...options.headers,
+    'x-routing-strategy': 'custom-router',
+  };
+
   return 'http://www.example.org'; // protocol + host
 };
 
@@ -30,6 +36,8 @@ const app = express();
 app.use(myProxy); // add the proxy to express
 
 app.listen(3000);
+
+// NOTE: `res` is undefined in WebSocket upgrade flows.
 ```
 
 ## Proxy Table
diff --git a/recipes/websocket.md b/recipes/websocket.md
index 6a24bdaf..a467a951 100644
--- a/recipes/websocket.md
+++ b/recipes/websocket.md
@@ -9,7 +9,9 @@ Examples to use `http-proxy-middleware` with WebSocket support.
 
 ## WebSocket - `ws:true` flag (automatic upgrade subscription)
 
-⚠️ NOTE: Using `ws: true` requires an an initial regular HTTP request, so HPM can subscribe to server upgrade event internally.
+⚠️ NOTE: Using `ws: true` requires an initial regular HTTP request, so HPM can subscribe to the server upgrade event internally.
+
+⚠️ NOTE: If the same middleware is attached to multiple servers, each server needs its own initial HTTP request before auto upgrade subscription is active.
 
 💡 Use `server.on('upgrade', proxy.upgrade)` without the need of an initial HTTP request.