diff --git a/doc/publican/sources/Protocol.xml b/doc/publican/sources/Protocol.xml
index 477063be..66cebfb6 100644
--- a/doc/publican/sources/Protocol.xml
+++ b/doc/publican/sources/Protocol.xml
@@ -14,6 +14,38 @@
       object implements an interface and the requests include an opcode that
       identifies which method in the interface to invoke.
     </para>
+    <para>
+      The protocol is message-based.  A message sent by a client to the server
+      is called request.  A message from the server to a client is called event.
+      A message has a number of arguments, each of which has a certain type (see
+      <xref linkend="sect-Protocol-Wire-Format"/> for a list of argument types).
+    </para>
+    <para>
+      Additionally, the protocol can specify <type>enum</type>s which associate
+      names to specific numeric enumeration values.  These are primarily just
+      descriptive in nature: at the wire format level enums are just integers.
+      But they also serve a secondary purpose to enhance type safety or
+      otherwise add context for use in language bindings or other such code.
+      This latter usage is only supported so long as code written before these
+      attributes were introduced still works after; in other words, adding an
+      enum should not break API, otherwise it puts backwards compatibility at
+      risk.
+    </para>
+    <para>
+      <type>enum</type>s can be defined as just a set of integers, or as
+      bitfields.  This is specified via the <type>bitfield</type> boolean
+      attribute in the <type>enum</type> definition.  If this attribute is true,
+      the enum is intended to be accessed primarily using bitwise operations,
+      for example when arbitrarily many choices of the enum can be ORed
+      together; if it is false, or the attribute is omitted, then the enum
+      arguments are a just a sequence of numerical values.
+    </para>
+    <para>
+      The <type>enum</type> attribute can be used on either <type>uint</type>
+      or <type>int</type> arguments, however if the <type>enum</type> is
+      defined as a <type>bitfield</type>, it can only be used on
+      <type>uint</type> args.
+    </para>
     <para>
       The server sends back events to the client, each event is emitted from
       an object.  Events can be error conditions.  The event includes the
@@ -62,14 +94,11 @@
       The protocol is sent over a UNIX domain stream socket, where the endpoint
       usually is named <systemitem class="service">wayland-0</systemitem>
       (although it can be changed via <emphasis>WAYLAND_DISPLAY</emphasis>
-      in the environment).  The protocol is message-based.  A
-      message sent by a client to the server is called request.  A message
-      from the server to a client is called event.  Every message is
-      structured as 32-bit words, values are represented in the host's
-      byte-order.
+      in the environment).
     </para>
     <para>
-      The message header has 2 words in it:
+      Every message is structured as 32-bit words; values are represented in the
+      host's byte-order.  The message header has 2 words in it:
       <itemizedlist>
 	<listitem>
 	  <para>