diff --git a/README.md b/README.md
index 9c5709a..32c6b43 100644
--- a/README.md
+++ b/README.md
@@ -27,24 +27,46 @@ The extension can be configured, for example:
 
 ```js
 var Extensions = require('websocket-extensions'),
-    deflate    = require('permessage-deflate');
+    deflate    = require('permessage-deflate'),
+    zlib       = require('zlib');
 
-deflate = deflate.configure({noContextTakeover: true});
+deflate = deflate.configure({
+  level: zlib.Z_BEST_COMPRESSION,
+  maxWindowBits: 13
+});
 
 var exts = new Extensions();
 exts.add(deflate);
 ```
 
-Supported options are:
+The set of available options can be split into two sets: those that control the
+session's compressor for outgoing messages and do not need to be communicated to
+the peer, and those that are negoatiated as part of the protocol. The settings
+only affecting the compressor are described fully in the [zlib
+documentation](http://nodejs.org/api/zlib.html#zlib_options):
+
+* `level`: sets the compression level, can be an integer from `0` to `9`, or one
+  of the contants `zlib.Z_NO_COMPRESSION`, `zlib.Z_BEST_SPEED`,
+  `zlib.Z_BEST_COMPRESSION`, or `zlib.Z_DEFAULT_COMPRESSION`
+* `memLevel`: sets how much memory the compressor allocates, can be an integer
+  from `1` to `9`, or one of the constants `zlib.Z_MIN_MEMLEVEL`,
+  `zlib.Z_MAX_MEMLEVEL`, or `zlib.Z_DEFAULT_MEMLEVEL`
+* `strategy`: can be one of the constants `zlib.Z_FILTERED`,
+  `zlib.Z_HUFFMAN_ONLY`, `zlib.Z_RLE`, `zlib.Z_FIXED`, or
+  `zlib.Z_DEFAULT_STRATEGY`
+
+The other options relate to settings that are negotiated via the protocol and
+can be used to set the local session's behaviour and control that of the peer:
 
 * `noContextTakeover`: if `true`, stops the session reusing a deflate context
   between messages
 * `requestNoContextTakeover`: if `true`, makes the session tell the other peer
   not to reuse a deflate context between messages
-* `maxWindowBits`: an integer from `8` to `15` inclusive that sets the size of
-  the session's sliding window
+* `maxWindowBits`: an integer from `8` to `15` inclusive that sets the maximum
+  size of the session's sliding window; a lower window size will be used if
+  requested by the peer
 * `requestMaxWindowBits`: an integer from `8` to `15` inclusive to ask the other
-  peer to use to set its sliding window size, if supported
+  peer to use to set its maximum sliding window size, if supported
 
 ## License