<?xml version='1.0'?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
                  "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" [

<!ENTITY Evolution "<application>Evolution</application>">
<!ENTITY GNOME "<application>GNOME</application>">
<!ENTITY eclipse "<application>Eclipse</application>">
<!ENTITY Camel "<application>Camel</application>">
<!ENTITY EPlugin "<application>EPlugin</application>">
<!ENTITY e-popup-reference SYSTEM "e-popup.xml">
<!ENTITY e-menu-reference SYSTEM "e-menu.xml">
<!ENTITY e-config-reference SYSTEM "e-config.xml">
<!ENTITY e-event-reference SYSTEM "e-event.xml">
<!ENTITY e-plugin-reference SYSTEM "e-plugin.xml">
<!ENTITY e-import-reference SYSTEM "e-import.xml">

<!ENTITY em-popup-reference SYSTEM "em-popup.xml">
<!ENTITY em-format-reference SYSTEM "em-format.xml">

<!ENTITY em-popups SYSTEM "em-popups.xml">
<!ENTITY em-menus SYSTEM "em-menus.xml">
<!ENTITY em-configs SYSTEM "em-configs.xml">
<!ENTITY em-events SYSTEM "em-events.xml">

<!ENTITY ecal-popups SYSTEM "ecal-popups.xml">

<!ENTITY es-events SYSTEM "es-events.xml">
<!ENTITY es-menus SYSTEM "es-menus.xml">
<!ENTITY es-importers SYSTEM "es-importers.xml">

]>
<?xml-stylesheet href="sdocbook.css" type="text/css"?>

<book lang="en">
  <!-- DocBook file was created by LyX 1.3
  See http://www.lyx.org/ for more information -->
  <bookinfo>
    <title>
      &Evolution; Plugin Development Manual
    </title>
    
    <authorgroup>
      <corpauthor>
	Novell, Inc.
      </corpauthor>
      <author>
	<firstname>Michael</firstname><surname>Zucchi</surname>
      </author>
    </authorgroup>

    <copyright>
      <year>2004</year>
      <holder>Novell, Inc.</holder>
    </copyright>

  </bookinfo>

  <preface id="preface">
    <title>Preface</title>

    <para>
      This document is work-in-progress.  Its structure and design is still as
      fluid as the underlying strucutre and design of some parts of EPlugin.
      There's no guarantee it will be updated at regular intervals,
      particularly this version.
    </para>
    <para>
      The API documentation is currently generated using the Linux kernel-doc
      script.  The stylesheets used to generate the HTML you're seeing seems to
      have bugs which duplicates some sections.  It is also ugly and difficult
      to navigate.
    </para>

    <sect1>
      <title>Conventions</title>
      <para>
	The following conventions are used in the manual ... (insert details
	here).
      </para>
      <sect2>
	<title>XML Annotation</title>
	<para>
	  XML definitions are annotated with BNF-style markers to indicate
	  alternative (|), multiples (* or +), and optional (?) items.  If no
	  annotation is present then the item must be present once.
	</para>
	<variablelist>
	  <varlistentry>
	    <!-- is symbol the right one here? -->
	    <term><symbol>|</symbol></term>
	    <listitem>
	      <simpara>Indicates an alternative option.  Only one of the items
		separated by <symbol>|</symbol> is to be chosen.
	      </simpara>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><symbol>*</symbol></term>
	    <listitem>
	      <simpara>Following an item, <symbol>*</symbol> indicates the item
		may occur any number of times, including no times (0 or more
		multiple).
	      </simpara>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><symbol>+</symbol></term>
	    <listitem>
	      <simpara>Following an item, <symbol>+</symbol> indicates the item
		must occur at least once, but may occur more than ones (1 or
		more multiple).
	      </simpara>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><symbol>?</symbol></term>
	    <listitem>
	      <simpara>Following an item, <symbol>?</symbol> indicates the item
		may occur at most once, if present (0 or 1 times).
	      </simpara>
	    </listitem>
	  </varlistentry>
	</variablelist>
      </sect2>
    </sect1>

  </preface>

  <part id="informational">
    <title>
      EPlugin
    </title>
    <chapter>
      <title>
	Introduction
      </title>
      <para>
	This book aims to be a comprehensive technical manual for the
	development of plugins for &Evolution;, a personal information manager
	for &GNOME;.
      </para>
      <para>
	Up-to, and including, &Evolution; version 2.0, &Evolution; contained
	limited extensibility interfaces. There were only two ways to extend
	&Evolution;; by implementing a new top-level component, or by
	implementing a &Camel; provider. When implementing a top-level component,
	there was still little integration, and in effect it was merely a more
	complex way of writing a separate &GNOME; application. &Camel; providers
	were only designed to be e-mail storage backends, so were of limited
	use for general extensibility. Despite this, both mechanisms were used
	for example for the Exchange Connector, although the system made the
	integration clumsy and difficult.
      </para>
      <para>
	This lack of extensibility has severaly stifled external developer
	contributions by forcing any extensions to be considered as core
	features. &Evolution; being a commercial product, it has tight usability
	and quality requirements that limits the ability to experiment with
	the core feature set in this way. As a result, very few lines of code
	or new features have been implemented by external contributors.
      </para>
      <para>
	One of the major goals for the 2.2 release was to implement an
	extensibility system, given the working name of EPlugin, which must
	provide a frame-work for both providing extensibility hooks, and for
	extending the functionality of &Evolution;.
      </para>
      <sect1>
	<title>
	  Plugin System
	</title>
	<para>
	  Any plugin system will generally have a number of goals:
	</para>
	<itemizedlist>
	  <listitem>
	    <simpara>
	      Provide a language independent invocation mechanism
	    </simpara>
	  </listitem>
	  <listitem>
	    <simpara>
	      Allow extension of parts of the user interface and processing elements
	    </simpara>
	  </listitem>
	  <listitem>
	    <simpara>
	      Require minimal extra or foreign code to implement in the core application
	    </simpara>
	  </listitem>
	  <listitem>
	    <simpara>
	      Require minimal interface code to implement the extensions
	    </simpara>
	  </listitem>
	  <listitem>
	    <simpara>
	      Not to impact performance or increase resource usage unduly
	    </simpara>
	  </listitem>
	  <listitem>
	    <simpara>
	      Versioning
	    </simpara>
	  </listitem>
	  <listitem>
	    <simpara>
	      Be able to be extended itself fairly easily.
	    </simpara>
	  </listitem>
	</itemizedlist>
	<para>
	  EPlugin manages to fulfill these goals in most cases. EPlugin isn't a
	  single object or interface in itself, although there is an object
	  titled EPlugin, it is a synergistic
	  <footnote><simpara>I've always wanted to use
	      <emphasis>synergistic</emphasis> in a sentence since
	      I read it on the back of the Commodore 64 Users
	      Guide.</simpara></footnote>
	  collection of integrated and
	  continually evolving objects which work together to achieve these
	  goals (and that will definitly be the end of the MarketSpeak). It
	  consists of a loader to invoke extension callbacks, hooks to resolve
	  these callbacks, targets to identify context, and managers which are
	  used by the core code to provide functionality and merging points for
	  the extensions.
	</para>
	<para>
	  EPlugin's design was inspired and influenced by the &eclipse;
	  project. It aims at a lower target however, so it was able more easily
	  implemented in a practical time-frame.
	</para>
	<para>
	  &EPlugin; was chosen as an approach to the problem of adding
	  scriptability to &Evolution;.  Instead of just linking to Perl, or
	  Python, or even Mono by itself an approach was taken which focuses on
	  the application end of the system.  So instead of making every part
	  of the application export its functionality and have to deal with
	  whatever script engine is present, EPlugin addresses the hooking part
	  of the equation in a language-independent manner.  It also attemps to
	  do it in a way which doesn't impact on the application development
	  either.
	</para>
	<para>
	  The EPlugin world is awash with its own language. The next few
	  sections will introduce the basic plugin nomenclature and high-level
	  view of this world.
	</para>

      </sect1>

      <sect1>
	<title>
	  Loaders
	</title>
	<para>
	  The core of EPlugin is a light-weight object loader and callback
	  invocation system. Because of the varied calling conventions of
	  different languages, and to reduce the overhead of the plugin system
	  itself, all callbacks only receive and return a single argument. By
	  using structures to pass complex arguments, native C plugins require
	  no extra overhead, and marshalling details are moved into the plugin
	  implementation itself where required. It also simplifies memory
	  management issues significantly. For example, the C plugin handler
	  merely loads a shared library using GModule, and resolves a symbol by
	  name; and is so all of 50 lines of code, total. The loaders are the
	  only modules which need to interace with non-native code or
	  conventions.
	</para>
	<para>
	  The other task of the plugin core is to load XML definitions of the
	  plugins. Extension hooks are registered with the plugin core before
	  the plugins are scanned, and are automatically instantiated to load
	  each definition appropriately as they are encountered.
	</para>
	<para>
	  At each layer, a level of indirection is used so that new loaders and
	  new hooks can be added transparently, and extend the plugin
	  definition freely with any information they require.
	</para>
      </sect1>

      <sect1>
	<title>
	  Hooks
	</title>
	<para>
	  The hooks
	  <footnote>
	    <para>A hook is something you can hang your stuff on.</para>
	  </footnote>
	  which are registered with the loader provide meta-data for
	  the management implementation layer for extending it at
	  run-time. Their primary
	  functions are to load the detail of the XML plugin definition, map it
	  to the implementation, and marshal the implementation callbacks to
	  the common plugin interface. How they do this depends on the
	  implementation itself, and ranges from registering factory methods to
	  simply adding the items directly.
	</para>
	<para>
	  In most cases the physical object need not be loaded until the
	  callback is invoked, since the plugin definitions provide enough
	  contextual information to build the interface or determine when they
	  need to be invoked.
	</para>
      </sect1>

      <sect1>
	<title>
	  Managers
	</title>
	<para>
	  Managers
	  <footnote>
	    <para>
	      Unlike real managers, these are the ones that do the heavy lifting.
	    </para>
	  </footnote>
	  provide tools for the core code to extend itself at specific
	  points, and in many cases are the objects used directly in the code
	  to implement core features. In other cases they simply provide the
	  hooks with an entry point into &Evolution;. For example, for the main
	  menu hook, the manager is a thin layer to BonoboUI. On the other
	  hand, EPopup is a complete implementation of a popup menu management
	  system which was already used in &Evolution; 2.0. Some managers are
	  one-off objects used as constructors for other objects, others are
	  view-dependent, and some are static objects, such as the Event
	  routers.
	</para>
      </sect1>

      <sect1>
	<title>
	  Items
	</title>
	<para>
	  Each manager uses a number of items to describe the object they
	  control or create. The items are added to each manager instance from
	  the plugins or from core code. The items from all of these sources
	  are then merged together when required and processed accordingly. For
	  example, menu items are merged into a tree of GtkMenus. Events on the
	  other hand are simply ordered and then invoked in the order of their
	  priority. Items are part of the manager implementation, and in
	  &EPlugin; they are all extensible objects too, which the hooks use to
	  perform mapping to the plugin. Items may be extended by code hooking
	  into the implementation, either the plugin hooks, or the core code.
	</para>
      </sect1>

      <sect1>
	<title>
	  Targets
	</title>
	<para>
	  Targets
	  <footnote><para>Think of a target as the target of
	      interest.</para></footnote>
	  are view or component specific context objects. They contain
	  enough information to be used as stand-alone contexts to implement
	  callbacks for both core functions and plugin hooks. For example for
	  the mail view, a select target contains a folder and a list of
	  selected messages. An attachment (part) target contains the
	  &Camel; representation of the part and the mime-type for
	  that part. Targets are part of the manager implementation and are
	  extended by subclassing the manager.
	</para>
      </sect1>
    </chapter>

    <chapter id="plugin-loaders">
      <title>
	Plugin Loaders
      </title>
      <para>
	Plugin loaders implement a hool to a new language, or loading system in the
	plugin system.  The actual binding of new languages to the plugin system or
	other parst of &Evolution;s api's are beyond the scope of this
	document, some languages make this easier than others.
      </para>
      <sect1 id="plugin-loaders-base">
	<title>
	  Base Plugin
	</title>
	<para>
	  The <link linkend="API-struct--EPlugin">EPlugin base class</link>
	  is an abstract class which provides the basic services for plugin
	  implementations. The main services are:
	  <itemizedlist>
	    <listitem><simpara>Resolve plugin type and instantiate an EPlugin
		object to represent and manage it.</simpara></listitem>
	    <listitem><simpara>Load the base structure of the XML plugin
		definition files.</simpara></listitem>
	    <listitem><simpara>Resolve plugin hook types and instantiate an
		EPluginHook to represent and manage it.</simpara></listitem>
	    <listitem><simpara>Provide a simple, language-independent api for
		invoking plugin callbacks</simpara></listitem>
	    <listitem><simpara>Provide I18N context for plugins.</simpara></listitem>
	    <listitem><simpara>Some simple static helper methods to simplify each
		implementing class.</simpara></listitem>
	  </itemizedlist>
	  See the <xref linkend="REF-EPlugin"/> for
	  these details.
	</para>

	<sect2 id="plugin-loaders-definition">
	  <title>Definition of a Plugin</title>
	  <para>
	    The base plugin XML definition.  Subclasses of EPlugin extend this
	    basic structure with additional parameters or elements as they
	    require.
	  </para>
	  <para>
	    Note that there may be any number of <sgmltag>e-plugin</sgmltag>
	    elements in a given plugin file, this may be used to simplify
	    distribution of plugin packages.
	  </para>
	  <programlisting>
	    <![CDATA[
<?xml version="1.0">
<e-plugin-list>
  <e-plugin
    id="unique id"
    type="loader type"
    domain="translation domain" ?
    localedir="locale directory" ?
    name="plugin name"
    ...>
    <description>long description</description> ?
    <author name="real name"? email="email addr"?/> *
    <hook
      class="hook class"
      ...>
    ...
    </hook> +
  </e-plugin> +
</e-plugin-list>]]></programlisting>
	  <variablelist>
	    <varlistentry>
	      <term><parameter>id</parameter></term>
	      <listitem>
		<simpara>
		  A unique string identifying this plugin.  By convention this
		  will follow the java-like class namespace system.
		  e.g. <constant>com.ximian.evolution.test-plugin</constant>
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>type</parameter></term>
	      <listitem>
		<simpara>
		  The type name of the plugin loader.  Currently <link
		    linkend="plugin-loaders-lib">shlib</link> and <link
		    linkend="plugin-loaders-mono">mono</link> are the only
		  supported values.  If no known handler is registered for this
		  type, the plugin definition is silently ignored.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>domain</parameter></term>
	      <listitem>
		<simpara>
		  The translation domain for this plugin, as passed to the
		  <function>dcgettext</function> call of the gettext package.
		  If not supplied then the default application domain is used
		  (i.e. &quot;evolution&quot;).  This is used to translate
		  translatable strings for display.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>localedir</parameter></term>
	      <listitem>
		<simpara>
		  If this and <parameter>domain</parameter> is defined, then
		  this is the directory of the locale information for this
		  domain.  It, and the <parameter>domain</parameter> will be
		  passed to  <function>bindtextdomain</function> before any
		  strings are translated.  See that function for more
		  information.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>name</parameter></term>
	      <listitem>
		<simpara>
		  A short name for the plugin.  &quot;Bob's Wonder
		  Extender&quot; might be suitable.  This value will be
		  translated.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>description</parameter></term>
	      <listitem>
		<simpara>
		  A longer description of the plugin's purpose. This value will be
		  translated.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>author</parameter></term>
	      <listitem>
		<simpara>
		  One of the authors who wrote the plugin.  Either
		  <parameter>name</parameter> or <parameter>email</parameter>
		  may be ommitted.  This element may occur multiple times to
		  indicate multiple authors.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>hook</parameter></term>
	      <listitem>
		<simpara>
		  This is a list of all of the hooks that this plugin wishes to
		  hook into.  See the <link linkend="plugin-hooks">Plugin
		    Hooks</link> section for the details of the basic hook
		  types defined.
		</simpara>
		<simpara>
		  The hook <parameter>class</parameter> is resolved using the
		  registered hook types, and if none can be found, or a version
		  mismatch occurs, then the hook is silently ignored.
		</simpara>
	      </listitem>
	    </varlistentry>
	  </variablelist>
	</sect2>
      </sect1>

      <sect1 id="plugin-loaders-lib">
	<title>
	  Shared Library Loader
	</title>
	<para>
	  The shared library loader <link
	    linkend="API-struct--EPluginLib">EPluginLib</link> implements a
	  concrete EPlugin type which loads GNU shared libraries via the
	  GModule api.  It simply resolves symbols directly from the loaded
	  shared object and invokes them expecting a function signature of
	  <type>EPluginLibFunc</type>.
	</para>
	<para>
	  To manage plugin lifecycle, the function
	  <function>e_plugin_lib_enable</function>
	  will be invoked which allows the plugin to initialise itself.  Its
	  signature should match <type>EPluginLibEnableFunc</type>, and it will
	  be called with <parameter>enable=1</parameter>.  If the enable
	  function returns non-zero it is assumed to have failed intialisation
	  and will not be invoked further.
	</para>

	<sect2 id="plugin-loaders-lib-definition">
	  <title>Definition</title>
	  <para>The shared library loader only requires one extra parameter in
	    the base plugin definition.
	  </para>
	  <programlisting>
	    <![CDATA[
<e-plugin
  ...
  type="shlib"
  location="/full/path/name.so"
  load-on-startup="true" ?
  ...
  <hook class="...">
   ...
</e-plugin>]]></programlisting>
	  <variablelist>
	    <varlistentry>
	      <term><parameter>type</parameter></term>
	      <listitem>
		<simpara>
		  The type name of the shared library plugin is
		  <constant>shlib</constant>.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>location</parameter></term>
	      <listitem>
		<simpara>
		  The location parameter contains
		  the full path-name of a shared object to load.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>load-on-startup</parameter></term>
	      <listitem>
		<simpara>
		  If provided, indicates that the plugin should be loaded and
		  enabled when the application is first started.  Normally the
		  plugin is only loaded when necessary, i.e. when a callback is
		  first invoked.  Only use this option if you have defined an
		  <function>e_plugin_lib_enable</function> callback in your
		  module, and only if absolutely necessary.
		</simpara>
	      </listitem>
	    </varlistentry>
	  </variablelist>
	</sect2>

	<sect2 id="plugin-loaders-lib-invocation">
	  <title>Invocation</title>
	  <simplesect>
	    <title>Function specification
	    </title>
	    <para>Where a function spec is required in a plugin
	      hook definition, it should simply be the full name of an
	      exported symbol in the shared object.
	    </para>
	  </simplesect>
	  <simplesect>
	    <title>Callback signature</title>
	    <funcsynopsis><funcprototype>
		<funcdef>void * <function>function</function></funcdef>
		<paramdef>EPlugin * <parameter>ep</parameter></paramdef>
		<paramdef>void * <parameter>data</parameter></paramdef>
	      </funcprototype></funcsynopsis>
	    <variablelist>
	      <varlistentry>
		<term><function>function</function></term>
		<listitem>
		  <simpara>
		    The callback function.
		  </simpara>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term><parameter>ep</parameter></term>
		<listitem>
		  <simpara>
		    The container EPlugin representing this plugin.
		  </simpara>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term><parameter>data</parameter></term>
		<listitem>
		  <simpara>
		    Hook context data.  It is part of the hook's api to specify
		    the type of this pointer.
		  </simpara>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term><returnvalue>return value</returnvalue></term>
		<listitem>
		  <simpara>
		    Return data.  It is part of the hook's api to specify the
		    type of this pointer.
		  </simpara>
		</listitem>
	      </varlistentry>
	    </variablelist>
	  </simplesect>
	</sect2>
      </sect1>

      <sect1 id="plugin-loaders-mono">
	<title>
	  Mono Assembly Loader
	</title>
	<para>
	  The mono assembly loader <link
	    linkend="API-struct--EPluginMono">EPluginMono</link> implements a
	  concrete EPlugin type which loads C# assemblies using Mono.  Apart
	  from loading the assembly, it can optionally instantiate a class to
	  implement the callback or invoke static methods directly.
	</para>

	<sect2 id="plugin-loaders-mono-definition">
	  <title>Definition</title>
	  <para>The mono assembly loader needs the name of the assembly and
	    optionally the name of the class for handling the callbacks.
	  </para>
	  <programlisting>
	    <![CDATA[
<e-plugin
  ...
  type="mono"
  location="/full/path/name.dll"
  handler="PluginClass" ?
  ...
  <hook class="...">
   ...
</e-plugin>]]></programlisting>
	  <variablelist>
	    <varlistentry>
	      <term><parameter>type</parameter></term>
	      <listitem>
		<simpara>
		  The type name of a mono assembly plugin is
		  <constant>mono</constant>.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>location</parameter></term>
	      <listitem>
		<simpara>
		  The location parameter contains
		  the full path-name of an assembly to load.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>handler</parameter></term>
	      <listitem>
		<simpara>
		  If supplied, the handler contains the fully qualified name of
		  the class which handles all callbacks for this plugin.  If a
		  handling class is used, then the function specifications
		  become relative to this class.
		</simpara>
		<simpara>
		  This class will be
		  instantiated once upon the first callback invocation, and
		  remain active for the life of the plugin (or application).
		</simpara>
	      </listitem>
	    </varlistentry>
	  </variablelist>
	</sect2>

	<sect2 id="plugin-loaders-mono-invocation">
	  <title>Invocation</title>
	  <simplesect>
	    <title>Function specification
	    </title>
	    <para>If no <parameter>handler</parameter> class is specified, then
	      the function specification must match a static method in the
	      assembly.  This is passed to <function>mono_method_desc_new</function>
	      and <function>mono_method_desc_search_in_image</function>,
	      typically <function>FunctionName(intptr)</function>.
	    </para>
	    <para>
	      If the handler is specified, then the function specification is
	      relative to the handler class.  This is passed to
	      <function>mono_method_desc_new</function> and
	      <function>mono_method_desc_search_in_class</function>, typically
	      <function>:MethodName(intptr)</function>.
	    </para>
	  </simplesect>
	  <simplesect>
	    <title>Callback signature</title>
	    <funcsynopsis><funcprototype>
		<funcdef>IntPtr <function>function</function></funcdef>
		<paramdef>IntPtr <parameter>data</parameter></paramdef>
	      </funcprototype></funcsynopsis>
	    <variablelist>
	      <varlistentry>
		<term><function>function</function></term>
		<listitem>
		  <simpara>
		    The callback method.
		  </simpara>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term><parameter>data</parameter></term>
		<listitem>
		  <simpara>
		    The hook context data.  This is a pointer to unmanaged data, and it is up-to the plugin to interpret this
		    data right now, although some helper binding classes are
		    planned.  FIXME: hook-up when they and doco are done.
		  </simpara>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term><returnvalue>return value</returnvalue></term>
		<listitem>
		  <simpara>
		    The callback return data.  It is up to the hook's api to
		    define the type of this pointer.  It may be a simple boxed
		    value type, or a memory pointer allocated in unmanaged memory (e.g. a
		    GObject handle or a CamelObject cobject value).
		  </simpara>
		</listitem>
	      </varlistentry>
	    </variablelist>
	  </simplesect>
	</sect2>
      </sect1>

    </chapter>

    <chapter id="plugin-hooks">
      <title>
	Plugin Hooks
      </title>
      <para>
	This chapter will introduce the available plugin hook types. A given
	plugin can hook into any of these hooks any number of times. Some refer
	to specific instances of objects and others are implicitly defined.
      </para>
      <para>
	By design, there is considerable similarity and orthogonality amongst
	all of the various hook types and management objects.
      </para>
      <sect1 id="plugin-hooks-popup">
	<title>
	  Popup Menus
	</title>
	<para>
	  The popup menu hook lets you hook into any of the context menus in
	  &Evolution;, by name and context. Complex, dynamic, and multi-level
	  menus are created on the fly by merging the items for a given menu as
	  it is being shown. Each component provides its own context targets to
	  self-describe the situation under which the menu is invoked. Plugins
	  and core code alike are then invoked at the user's direction. The
	  popup manager and all context data lives as long as the menu and
	  until a choice is made, simplifying memory management.
	</para>
	<para>
	  The menu is merged from multiple plugins and core application code by
	  using a simple lexiographical sort of an absolute path to the menu
	  item. This merged list is then scanned and expanded into a tree of
	  menus. Individual items can be hidden or inactive based on the target
	  and a simple mask which is defined by the component itself. A rich
	  collection of menu item types are possible, from simple, to
	  checkboxes or images. The popup code is simple, and easy to use, and
	  simplifies the use of popup menu's in the core application anyway,
	  that they are pluggable is a free-bonus.
	</para>
	<sect2>
	  <title>Defining a popup hook</title>
	  <para>
	    Not sure if this fits here as such.  Probably temporary placeholder.
	  </para>
	  <programlisting>
	    <![CDATA[
<hook class="com.ximian.evolution.mail.popup:1.0">
 <menu id="menuid" target="targettype" factory="function spec"? >
  <item
   type="item | toggle | radio | image | submenu | bar"
   active ?
   path="foo/bar"
   label="menu text"
   icon="icon name" ?
   visible="target mask" ?
   enable="target mask" ?
   activate="function spec"/> *
 </menu> *
</hook>]]></programlisting>
	  <!-- this is all too bloody verbose, is there a better way? -->
	  <para>
	    <emphasis>Menu Tag</emphasis>
	  </para>
	  <variablelist>
	    <varlistentry>
	      <term><parameter>id</parameter></term>
	      <listitem>
		<simpara>
		  The id of the menu to which these items should be added.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>target</parameter></term>
	      <listitem>
		<simpara>
		  The target expected.  There will normally only be one target
		  type defined for any given menu, however some menu's may
		  supply multiple targets depending on context.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>factory</parameter></term>
	      <listitem>
		<simpara>
		  If present, then a plugin-specific function specification of
		  the function to invoke when the menu is being
		  created.  This function will normally call
		  e_popup_add_items() to add custom menu items.  It is used to
		  provide more control than the visible and enable masks
		  provide.  The plugin argument is the popup target.
		</simpara>
	      </listitem>
	    </varlistentry>
	  </variablelist>
	  <variablelist>
	    <varlistentry>
	      <term><parameter>type</parameter></term>
	      <listitem>
		<simpara>
		  The menu item type.  The type maps directly to the
		  corresponding EPopupItem types.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>active</parameter></term>
	      <listitem>
		<simpara>
		  If present, then radio or toggle menu items are active when
		  first shown.  After the first instantiation, they will
		  remember their active state.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>path</parameter></term>
	      <listitem>
		<simpara>
		  A '/' separated path used to position the item within menu
		  and in the right submenu.  Each menu and plugin should
		  define how its menu's are layed out so other plugins can
		  determine what value to use here.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>label</parameter></term>
	      <listitem>
		<simpara>
		  The text to be displayed on the menu item.  This will be
		  translated based on the plugin translation domain.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>icon</parameter></term>
	      <listitem>
		<simpara>
		  The name of a gnome-icon-theme standard icon, or the full
		  path-name of an icon image to use as menu item icon.  This
		  will be blank if not supplied.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>visible</parameter></term>
	      <listitem>
		<simpara>
		  A comma separated list of mask enumeration values used to
		  define when this item is shown.  What values are valid
		  depend on the menu hook class of the menu being hooked
		  onto.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>enable</parameter></term>
	      <listitem>
		<simpara>
		  A comma separated list of mask enumeration values used to
		  define when this item is enabled.  What values are valid
		  depend on the menu hook class of the menu being hooked
		  onto.  This is currently unimplemented.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>activate</parameter></term>
	      <listitem>
		<simpara>
		  A plugin-type specific function specification.  This
		  function will be resolved and called when the menu item is
		  activated.
		</simpara>
	      </listitem>
	    </varlistentry>
	  </variablelist>
	</sect2>
	<sect2>
	  <title>Merging Plugin Items</title>
	  <para>
	    A very simple algorithm is used to form the menu by merging the
	    plugin's menu items with the system menu items for a given menu.
	    What follows is a simple example of how this is done.  It will be
	    demonstrated using a simplified menu from the message-list, as used
	    in the &Evolution; Mail component, and a simple plugin which adds a
	    single menu item and menu separator into the middle of the menu,
	    when appropriate.
	  </para>
	  <para>
	    When the application wishes to show a specific popup menu, it
	    creates a new EPopup object with a unique menu id to manage it.  It
	    adds all of the items it wishes to add to the menu (see "Builtin
	    Items" in the following diagrams).  The application then asks for
	    the menu to be created.  The menu building
	    process adds all of the menu items from all plugins that target
	    this specific menu into a flat list, discarding those which don't
	    match the current Target qualifications.  The result is then
	    sorted using a simple ASCII sort, and then a menu built from the
	    remaining items.  This is probably best described by some diagrams.
	  </para>
	  <para>
	    The following two diagrams show how a popup menu is automatically
	    customised depending on the context.  On the left of each diagram
	    are all of the menu items which apply to the example menu.  The
	    menu label, with the qualifiers listed underneath, with the menu
	    item path along-side.  On the right-hand side of each diagram is
	    the result of:
	  </para>
	  <itemizedlist>
	    <listitem><simpara>Selecting items based on the target
		qualifiers</simpara></listitem>
	    <listitem><simpara>Sorting the remaining items based on their
		path.</simpara></listitem>
	    <listitem><simpara>Building this sorted list into a
		menu.</simpara></listitem>
	  </itemizedlist>

	  <para>
	    The actual list of target qualifiers are defined by the application
	    itself.  Generally a specific menu will have only one possible
	    target, and a list of matching target qualifiers.  The example
	    shows how a plugin can insert a menu item anwhere it wishes in the
	    menu system.  Submenus are also supported, and they work in exactly
	    the same manner, with / characters used to separate submenu paths.
	    A submenu must sort into the position immediately before the
	    definition of its items.
	  </para>

	  <figure id="e-popup-merge-1">
	    <title>Merging a menu with many items selected.</title>
	    <mediaobject>
	      <imageobject>
		<imagedata fileref="images/e-popup-merge-1.pic" format="PIC" />
	      </imageobject>
	      <imageobject>
		<imagedata fileref="images/e-popup-merge-1.eps" format="EPS"/>
	      </imageobject>
	      <imageobject>
		<imagedata fileref="images/e-popup-merge-1.png" format="PNG"/>
	      </imageobject>
	      <textobject>
		<phrase>Showing how a display list of menu items is selected
		  and then sorted for display.</phrase>
	      </textobject>
	    </mediaobject>
	  </figure>

	  <para>
	    The first diagram shows when the target qualifiers are
	    <parameter>many</parameter>, and
	    <parameter>mark_unread</parameter>.  The menu items which operate
	    on only one selected message are not shown.  Similarly for those
	    able to be marked as unread (i.e. they are currently read).
	  </para>

	  <figure id="e-popup-merge-2">
	    <title>Merging a menu with one item selected.</title>
	    <mediaobject>
	      <imageobject>
		<imagedata fileref="images/e-popup-merge-2.pic" format="PIC"/>
	      </imageobject>
	      <imageobject>
		<imagedata fileref="images/e-popup-merge-2.eps" format="EPS"/>
	      </imageobject>
	      <imageobject>
		<imagedata fileref="images/e-popup-merge-2.png" format="PNG"/>
	      </imageobject>
	      <textobject>
		<phrase>Showing how a display list of menu items is selected
		  and then sorted for display with different qualifiers.</phrase>
	      </textobject>
	    </mediaobject>
	  </figure>

	  <para>
	    This diagram shows when the target qualifiers are
	    <parameter>one</parameter>, and
	    <parameter>mark_read</parameter>.  The menu items which operate
	    on only many selected messages are not shown.  Similarly for those
	    able to be marked as read.
	  </para>
	</sect2>
      </sect1>

      <sect1 id="plugin-hooks-menu">
	<title>
	  Main menus
	</title>
	<para>
	  The main menu hook lets you hook into various main menus in
	  &Evolution;, based on the current active view (component). The system
	  works by piggy-backing on the existing use of the BonoboUI menu
	  system used by all of the &Evolution; components. Bonobo handles the
	  menu merging and user input, and the hook resolves the verb being
	  invoked and redirects it to the plugin. Each view defines a single
	  target which describes the appropriate context. For the Mail view,
	  this is the current folder and currently selected message(s).
	</para>
	<para>
	  Each view keeps track of its own manager object. When it is
	  (de)activated, it also (de)activates the management object which
	  dynamically adds and removes the menu items from the
	  BonoboUIContainer via a supplied BonoboUI XML definition file
	  &lt;perhaps it should embed the bonobouixml&gt;. If the target
	  changes, the view lets the manager know, and it updates the
	  visibility and sensitivity of objects appropriately, allowing
	  reasonably dynamic user-interfaces to be managed automatically. The
	  plugin itself isn't loaded until the menu item in question is invoked
	</para>
	<para>
	  Simple menu items and toggle menu items are supported currently.
	  Also, because actual menu display is driven by BonoboUI, then toolbar
	  items can also be added using this mechanism.
	</para>
	<sect2>
	  <title>Defining a menu hook</title>
	  <para>
	    Not sure if this fits here as such.  Probably temporary placeholder.
	  </para>
	  <programlisting>
	    <![CDATA[
<hook class="com.ximian.evolution.mail.bonoboMenu:1.0">
 <menu id="menuid" target="targettype"
  <ui file="/path/to/bonobo-ui-menu-definition.xml"> +
  <item
   type="item | toggle | radio"
   active ?
   path="/commands/FooBar"
   verb="FooBar"
   visible="target mask" ?
   enable="target mask" ?
   activate="function spec"/> *
 </menu> *
</hook>]]></programlisting>
	  <para>
	    <emphasis>Need to define menu tag</emphasis>
	  </para>
	  <variablelist>
	    <varlistentry>
	      <term><parameter>ui</parameter></term>
	      <listitem>
		<simpara>
		  The <parameter>ui</parameter> element contains a filename of the
		  BonoboUI XML menu definition to load when the view is activated.  Any number of
		  <parameter>ui</parameter> elements may be defined, and they
		  are all loaded.
		</simpara>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><parameter>type</parameter></term>
	      <listitem>
		<simpara>
		  The menu item type.  The type maps directly to the
		  corresponding EMenuItem types.
		  <parameter>radio</parameter> is currently not implemented.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>active</parameter></term>
	      <listitem>
		<simpara>
		  If present, then radio or toggle menu items are active when
		  first shown.  After the first instantiation, they will
		  remember their active state.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>path</parameter></term>
	      <listitem>
		<simpara>
		  The BonoboUI element path corresponding to this menu item.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>verb</parameter></term>
	      <listitem>
		<simpara>
		  The BonoboUI verb corresponding to the item to be listened to.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>visible</parameter></term>
	      <listitem>
		<simpara>
		  A comma separated list of mask enumeration values used to
		  define when this item is shown.  What values are valid
		  depend on the menu hook class of the menu being hooked
		  onto.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>enable</parameter></term>
	      <listitem>
		<simpara>
		  A comma separated list of mask enumeration values used to
		  define when this item is sensitive.  What values are valid
		  depend on the menu hook class of the menu being hooked
		  onto.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>activate</parameter></term>
	      <listitem>
		<simpara>
		  A plugin-type specific function specification.  This
		  function will be resolved and called when the menu item is
		  activated.  The funciton's parameters will depend on the type
		  of menu item being invoked.
		</simpara>
	      </listitem>
	    </varlistentry>
	  </variablelist>
	</sect2>
	<sect2>
	  <title>Merging Plugin Items</title>
	  <para>
	    Merging is performed by BonoboUI, and the source of the menu data
	    is defined by the <parameter>ui</parameter> file.
	  </para>
	</sect2>
      </sect1>

      <sect1 id="plugin-hooks-config">
	<title>
	  Configuration Pages and Wizards
	</title>
	<para>
	  Configuration pages are somewhat more complex than any of the other
	  types of hookable object. This is reflected in the complexity of the
	  items and callbacks involved.
	</para>
	<para>
	  Essentially, the EConfig object is used in combination to both
	  instrument existing windows and building new content.  Each
	  configuration window comprises of several basic elements with some
	  minor variations allowed.  It consists of a number of pages in a
	  specific order, each containing a number of titled sections in a specific
	  order, each containing a number of items.  The variations are that
	  the top-level widget may be a GtkNotebook or a GnomeDruid; and each
	  section may instrument a GtkBox, or a GtkGrid.  The definition of
	  the available hooks will define what form they take.
	</para>
	<para>
	  The EConfig manager uses the description of all the items supplied to
	  it to build the complete window.  It can also drive various aspects
	  of the UI, such as navigating through a druid or handling
	  instant-apply vs. modify-and-save dialogues.
	</para>
	<figure id="e-config-flow">
	  <title>Event and Data Flow in EMConfig</title>
	  <mediaobject>
	    <imageobject>
	      <imagedata fileref="images/e-config-flow.pic" format="PIC"/>
	    </imageobject>
	    <imageobject>
	      <imagedata fileref="images/e-config-flow.eps" format="EPS"/>
	    </imageobject>
	    <imageobject>
	      <imagedata fileref="images/e-config-flow.png" format="PNG"/>
	    </imageobject>
	    <textobject>
	      <phrase>The flow of information and control signals in the
		configuration management object.</phrase>
	    </textobject>
	  </mediaobject>
	</figure>

	<sect2>
	  <title>Defining a configuration page hook</title>
	  <para>
	    Not sure if this fits here as such.  Probably temporary placeholder.
	  </para>
	  <programlisting>
	    <![CDATA[
<hook class="com.ximian.evolution.mail.config:1.0">
 <group
  id="window id"
  target="targettype"
  check="function spec"?
  commit="function spec"?
  abort="function spec"?>
  <item
   type="book | druid | page | page_start | page_finish | section | section_grid | item | item_grid"
   path="/absolute/path"
   label="name" | factory="function  spec"
  /> *
 </menu> *
</hook>]]></programlisting>

	  <sect3>
	    <title>Group Element Properties</title>

	    <variablelist>
	      <varlistentry>
		<term><parameter>id</parameter></term>
		<listitem>
		  <simpara>
		    The name of the configuration window to which this hook
		    applies.
		  </simpara>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term><parameter>target</parameter></term>
		<listitem>
		  <simpara>
		    The type of target this configuration window applies too.
		    This will normally be tied directly to the specific
		    configuration window itself.
		  </simpara>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term><parameter>check</parameter></term>
		<listitem>
		  <simpara>
		    A callback which will be invoked to validate the
		    configuration or a specific page of the configuration.  It
		    will be invoked with a
		    <link
		      linkend="API-struct--EConfigHookPageCheckData">EConfigHookPageCheckData</link>
		    structure, and is expected to return a non-NULL value if
		    the page validates.
		  </simpara>
		  <simpara>
		    The callback will be expected to handle all
		    <parameter>pageid</parameter>'s present in the
		    configuration window, and should return
		    <constant>TRUE</constant> for pages it does not recognise.
		    If <parameter>pageid=&quot;&quot;</parameter> (an empty
		    string), then the <parameter>check</parameter> function
		    should validate all settings.  See also <xref
		      linkend="API-e-config-add-page-check" />.
		  </simpara>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term><parameter>commit</parameter></term>
		<listitem>
		  <simpara>
		    A callback which will be invoked to commit the
		    configuration data, if the configuration page isn't an
		    instant-apply one.  This callback can write any
		    configuration changes to permanent storage.  It is not used
		    for instant-apply windows.
		  </simpara>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term><parameter>abort</parameter></term>
		<listitem>
		  <simpara>
		    A callback which will be invoked to abort the configuration
		    process.  This callback is called when the
		    <guibutton>Cancel</guibutton> button is pressed on stateful
		    configuration windows.
		  </simpara>
		</listitem>
	      </varlistentry>
	    </variablelist>
	  </sect3>
	  <sect3>
	    <title>Item Element Properties</title>

	    <variablelist>
	      <varlistentry>
		<term><parameter>type</parameter></term>
		<listitem>
		  <simpara>
		    The menu item type.  The type maps directly to the
		    corresponding EConfigItem types.  Only one of
		    <parameter>book</parameter> and <parameter>druid</parameter>
		    may be supplied for the entire configuration page, and this
		    will usually already be defined by the application.
		  </simpara>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term><parameter>path</parameter></term>
		<listitem>
		  <simpara>
		    The path to the configuration item in question.  This is a
		    simple string that when sorted using an ASCII sort will place
		    the items in the right order.  That is, sections before items
		    before pages before the root object.
		  </simpara>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term><parameter>label</parameter></term>
		<listitem>
		  <simpara>
		    The textual label of this item.  This may only be supplied
		    for the section and page types.  For sections it will be the
		    section frame text.  For pages this will be the druid page
		    title or the notebook tab text.  If a
		    <parameter>factory</parameter>is supplied then this value is
		    not used.  This will be translated based on the plugin
		    translation domain.
		  </simpara>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term><parameter>factory</parameter></term>
		<listitem>
		  <simpara>
		    If supplied, the factory method used to create the GtkWidget
		    elements for this configuration item.  Factories may be
		    supplied for any of the item types.  If no
		    <parameter>label</parameter> is set then the
		    <parameter>factory</parameter> must be set.
		  </simpara>
		</listitem>
	      </varlistentry>
	    </variablelist>
	  </sect3>
	</sect2>
	<sect2>
	  <title>Generating Configuration Pages</title>
	  <para>
	    Configuration items essentially spam 3 dimensions, but are
	    merged in a similar fashion to the way Popup items are merged.  The
	    main difference is that there are no target qualifiers used to
	    select which items are shown, it is up to the item factory to
	    either create or not create the item as it sees fit.  The EConfig
	    manager takes care of the rest, including removing un-used sections
	    or pages.
	  </para>
	  <para>
	    All items for a given configuration screen are converted into a
	    list and sorted based on the <parameter>path</parameter>.  The
	    configuration builder then goes through each item, creating
	    container widgets or calling factories as required.  If a given
	    page or section is empty, then it is removed automatically.  This
	    process isn't only a one-off process.  For certain complex
	    configuration screens, items or even pages and sections need to be
	    dynamic based on a previous setting.  EConfig supports this mode of
	    operation too, in which case it re-builds the configuration screen
	    the same way, and automatically destroys the old widgets
	    <footnote><simpara>In most cases, in some cases additional manual
		processing is required in the factory
		callback.</simpara></footnote> and even re-orders pages and
	    sections where appropriate to make the user-interface consistent.
	  </para>
	  <para>
	    The following few examples some of the flexibility of the EConfig
	    system.
	  </para>
	  <figure id="e-config-build-1">
	    <title>The application defined, unaltered configuration page.</title>
	    <mediaobject>
	      <!-- do we need to build our own eps for the image? -->
	      <imageobject>
		<imagedata fileref="images/e-config-build-1.png" format="PNG"/>
	      </imageobject>
	      <textobject>
		<phrase>Shows the original HTML Mail settings page.</phrase>
	      </textobject>
	    </mediaobject>
	  </figure>
	  <para>
	    First we have the original configuration window.  This is defined
	    by the application, the application uses EConfig to build this
	    window, and in the process EConfig instruments the sections that
	    the application defines.  This allows plugins to add new
	    pages/sections/items anywhere on the page - to a granularity as
	    defined by the application.  For example the application may at
	    minimum merely define the top-level notebook or druid object and a
	    number of pages.  When the pages are created the application could
	    add as much content as it wants, which would still allow plugins to
	    extend the user interface, but only by adding options to the end of
	    each page.  At the other end of the scale the application could
	    enumerate every single item (i.e. row) in every section on every
	    page, allowing plugins to put new items anywhere in the display.
	  </para>
	  <figure id="e-config-build-2">
	    <title>A plugin adding a new section to an existing page.</title>
	    <mediaobject>
	      <!-- do we need to build our own eps for the image? -->
	      <imageobject>
		<imagedata fileref="images/e-config-build-2.png" format="PNG"/>
	      </imageobject>
	      <textobject>
		<phrase>Shows the HTML Mail settings page with a new section
		  and item added by a plugin.</phrase>
	      </textobject>
	    </mediaobject>
	  </figure>
	  <para>
	    In this case the plugin has merely added a new section on the
	    bottom of the HTML Mail settings page.  When the factory is called
	    the plugin has a parent GtkGrid (in this case, it could be a VBox)
	    and borderless frame already defined, and it just has to
	    instantiate its own control widgets, add them to the table, and
	    return one of the widgets.  The returned widget is used later if
	    the window needs to be reconfigured, although this particular configuration
	    page is static so it isn't needed.
	  </para>
	  <figure id="e-config-build-3">
	    <title>A plugin inserting a new page for its settings.</title>
	    <mediaobject>
	      <!-- do we need to build our own eps for the image? -->
	      <imageobject>
		<imagedata fileref="images/e-config-build-3.png" format="PNG"/>
	      </imageobject>
	      <textobject>
		<phrase>Shows the plugin adding a new page for its setting as
		  an alternative.</phrase>
	      </textobject>
	    </mediaobject>
	  </figure>
	  <para>
	    And finally we have exactly the same plugin, which has exactly the
	    same code.  But a small change to the plugin definition allows the
	    plugin to add an arbitrary new page (in an arbitrary position) into
	    the whole window.  If this was a druid, then new druid pages can
	    also be inserted at arbitrary locations, and page navigation (in a
	    strictly linear manner) is automatically controlled by EConfig as
	    per <xref linkend="e-config-flow"/>.
	  </para>
	  <para>
	    In practice, EConfig provides more than it takes the application to
	    use - generally little or no extra application code is required to
	    use it.  It also
	    <footnote><simpara>Or it will - the code needs some
		tweaking.</simpara></footnote> enforces and simplifies HIG
	    compliance.  And as a side-benefit to the application it
	    transparently provides extension hooks for
	    external code to provide a seamlessly integrated user experience.
	  </para>
	</sect2>
      </sect1>

      <sect1 id="plugin-hooks-event">
	<title>
	  Events
	</title>
	<para>
	  No extensibility framework would be complete without an event
	  system. Events are used to reflect changes in internal state of the
	  application, and track actions by the user. They can contain any
	  information and additionally can be filtered based on the information
	  itself. Special targets are used, as in the other plugin hooks, to
	  hold this information.
	</para>
	<para>
	  Event managers are defined to contain the different event types that
	  a given component can export. Only one event manager object is
	  instantiated for each component, and each plugin listening to events
	  from that component are registered on that event manager directly.
	</para>
	<para>
	  Events handlers have priorities, and can swallow events, allowing
	  some level of complexity of event routing. This feature might not
	  prove useful and may be removed in the future if it isn't.
	</para>
	<sect2>
	  <title>Defining an event hook</title>
	  <para>
	    Not sure if this fits here as such.  Probably temporary placeholder.
	  </para>

	  <programlisting>
	    <![CDATA[
<hook class="com.ximian.evolution.mail.events:1.0">
 <event
   target="target name"
   id="event name"
   type="pass | sink" ?
   priority="signed integer" ?
   enable="target mask" ?
   handle="function spec"/> *
</hook>]]></programlisting>
	  <variablelist>
	    <varlistentry>
	      <term><parameter>target</parameter></term>
	      <listitem>
		<simpara>
		  The target type of the event listener.  This will normally
		  match in a 1:1 relationship to the event
		  <parameter>id</parameter> itself.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>id</parameter></term>
	      <listitem>
		<simpara>
		  The name of the event to listen to.  By convention the names
		  will be of the form
		  <constant>target.event</constant>.
		  e.g. <constant>folder.changed</constant>, or
		  <constant>message.read</constant>, etc.  Although they are
		  just simple case-sensitive strings.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>type</parameter></term>
	      <listitem>
		<simpara>
		  The event listener type.  The type maps directly to the corresponding
		  corresponding EEventItem types.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>priority</parameter></term>
	      <listitem>
		<simpara>
		  A signed integer specifying the priority of this event
		  listener.  0 (zero) should be used normally, although positive
		  and negative integers in the range -128 to 127 may aslo be
		  used.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>enable</parameter></term>
	      <listitem>
		<simpara>
		  A comma separated list of mask enumeration values used to
		  qualify when this event listener is invoked.  What values are valid
		  depend on the event hook class.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>handle</parameter></term>
	      <listitem>
		<simpara>
		  A plugin-type specific function specification.  This
		  function will be resolved and called when an event is routed to
		  this listener.
		</simpara>
	      </listitem>
	    </varlistentry>
	  </variablelist>
	</sect2>
      </sect1>

      <sect1 id="plugin-hooks-format">
	<title>
	  Mail Formatter
	</title>
	<para>
	  The mail formatter plugin will invoke plugin code to format any part
	  of an email based on mime-type. There are several formatters used
	  internally by the mailer for different contexts, and each can be
	  hooked into separately, providing extensible mail formatting for
	  everything from the primary mail display, to printing, to reply
	  quoting and more. If you are implementing a handler for a given
	  mime-type, each formatter appropriate for the data-type should be
	  hooked into, so that it displays properly in all contexts.
	</para>
	<para>
	  Since the management object in this case is the same formatting
	  object as used by the core mail display engine, a plugin may override
	  or reimplement complete new functionality seamlessly.
	</para>
	<para>
	  This plugin hook isn't strictly part of the core functionality as it
	  is provided only by the mail component. It however demonstrates that the
	  plugin system is extensible itself.
	</para>
	<sect2>
	  <title>Defining a formatter hook</title>
	  <para>
	    Not sure if this fits here as such.  Probably temporary placeholder.
	  </para>

	  <programlisting>
	    <![CDATA[
<hook class="com.novell.evolution.mail.format:1.0">
 <group id="formatter type">
  <item
    flags="handler flags"
    mime_type="major/minor"
    format="function spec"/> +
 </group> +
</hook>]]></programlisting>
	  <variablelist>
	    <varlistentry>
	      <term><parameter>id</parameter></term>
	      <listitem>
		<simpara>
		  The actual formatter this applies to.  e.g. EMFormat for the
		  base formatter class, EMFormatHTML for HTML output to a
		  GtkHTML object, etc.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>flags</parameter></term>
	      <listitem>
		<simpara>
		  Flags to define whether this is an attachment or inline
		  content.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>id</parameter></term>
	      <listitem>
		<simpara>
		  The name of the event to listen to.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>mime_type</parameter></term>
	      <listitem>
		<simpara>
		  The type of object this handler formats.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>format</parameter></term>
	      <listitem>
		<simpara>
		  A plugin-type specific function specification.  This
		  function will be invoked to format objects of the specified
		  <parameter>mime_type</parameter>.
		</simpara>
	      </listitem>
	    </varlistentry>
	  </variablelist>
	</sect2>

	<sect2>
	  <title>The formatting process</title>
	  <para>
	    The formatting process is driven by the <link
	      linkend="API-struct--EMFormat">EMFormat</link> object, although
	    there are different subclasses of this object used for different
	    purposes.  These behave quite differently so each must be explained
	    separately.  There is the basic formatter type which converts a
	    CamelMimeMessage into a stream of data, and there is a HTML
	    <link linkend="API-struct--EMFormatHTML">formatter type</link>
	    which uses a GtkHTML object to parse the content
	    and may request further information required to complete the
	    formatting.
	  </para>
	  <para>
	    A basic formatter goes through the following steps:
	  </para>
	  <orderedlist>
	    <listitem>
	      <simpara>Outputs pre-amble information.  e.g. Flag-For-Followup
		status.  The pre-amble renderer is chosen using the pseudo
		mime-type <constant>x-evolution/message/prefix</constant>, and can be
		overridden or added to by plugging in to that type.</simpara>
	    </listitem>
	    <listitem>
	      <simpara>Looks up a handler for the pseudo mime-type
		<constant>x-evolution/message/rfc822</constant> and invokes it
		to begin message formatting.  The default handler displays the
		message headers and then formats the message contents.
	      </simpara>
	    </listitem>
	    <listitem>
	      <simpara>Using the mime-type of the content object (whether
		supplied or calculated), a handler is looked up from a
		per-class table to process the type.</simpara>
	    </listitem>
	    <listitem>
	      <simpara>If no handler exists, then the data is formatted as an
		attachment.</simpara>
	    </listitem>
	    <listitem>
	      <simpara>If a handler exists, then it is invoked to display that
		type.  Depending on whether the data is to be displayed
		'inline' or not, the data may also get an attachment expander
		and button.</simpara>
	    </listitem>
	    <listitem>
	      <simpara>The handler transforms the part's data, if need be, and
		writes the appropriate format output to a stream.</simpara>
	    </listitem>
	  </orderedlist>
	  <para>
	    For conglomerate types, the formatting process is continued
	    recursively, until all parts have been displayed, as appropriate.
	  </para>
	  <para>
	    A HTML formatter goes through the same basic steps, but has
	    additional features and requirements.  It uses multiple
	    threads.  At least one other thread is used for all of the
	    Camel message content operations since some of them may block on
	    remote I/O.  This also simplifies cancellation processing.  Also,
	    because it has access to a full HTML rendering object, references
	    to embedded content (images, buttons, etc.) are also processed.
	  </para>
	  <para>
	    Most format handlers don't need to know about all the fiddly
	    details however.  If they are just outputting HTML content with no
	    out of band references, they work identical to the basic format
	    handlers with the exception they cannot call any Gtk GUI code
	    because of threading issues.  This can still be done by using an
	    IFRAME.  If they want to embed an icon or other image,
	    they simply need to insert the HTML IMG tag reference in their
	    format handler, and setup a callback to handle it when GtkHTML
	    requests it.  EMFormat has some helper classes to make this
	    only a few lines of code, including generation of the IMG SRC URL.
	    IFRAMEs work identically to IMG tags, and  similar process is
	    involved with embedding custom widgets using the OBJECT tag.
	    EMFormatHTML takes care of calling the right callbacks for the
	    right embedded reference from the right thread.
	  </para>
	  <para>
	    Since format handlers are chained off a given type, then a plugin
	    can also inherit formatting behaviour as well as override it.  This
	    gives much greater flexibility since the plugin need only implement
	    its behaviour in specific situations.  e.g. an OpenPGP message
	    handler could fall-back to the normal text-formatter if it doesn't
	    detect the ASCII armour in a text/plain part.  Or another handler
	    may disable itself based on configuration or state.
	  </para>
	  <para>
	    All format handlers for all types must also be fully re-entrant
	    code (more or less write-once global and static variables) if
	    they call any other formatting functions.
	  </para>
	</sect2>
      </sect1>

      <sect1 id="plugin-hooks-import">
	<title>
	  Importers
	</title>
	<para>
	  Importers let &Evolution; import data from other or older programs
	  into its native format.
	</para>
	<para>
	  Importers are driven from a druid in the shell, they can work on
	  individual files, or multiple component application data.  All
	  importers go through the same interface, is this data
	  present/supported, how do you control the import, and import the data.
	</para>
	<sect2>
	  <title>Defining an import hook</title>
	  <programlisting>
	    <![CDATA[
<hook class="org.gnome.evolution.import:1.0:1.0">
 <importer
   target="home | uri"
   supported="funcion spec"
   get-widget="function spec" ?
   import="function spec"
   cancel="function spec" ?
   name="name"
   description="description" ?/> *
</hook>]]></programlisting>
	  <variablelist>
	    <varlistentry>
	      <term><parameter>target</parameter></term>
	      <listitem>
		<simpara>
		  The target type for this importer.  File importers are of a
		  type <constant>uri</constant> and application importers are
		  of type <constant>home</constant> (indicating a 'home
		  directory').
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>supported</parameter></term>
	      <listitem>
		<simpara>
		  A function to call to determine if the file is supported or
		  not.  The function will be passed the target, and returns
		  non-NULL if the file is known or the application data exists.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>get-widget</parameter></term>
	      <listitem>
		<simpara>
		  A factory method to get a widget to control the import.  For
		  file-based importers, this should return a widget which lets
		  the user select the destination for the import.  For
		  application importers this should return a widget which lets
		  the user choose what to import.  Where possible, the
		  application importer should record whether or not the data
		  has already been imported and default any checkboxes
		  accordingly.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>import</parameter></term>
	      <listitem>
		<simpara>
		  The function to call to import the data.  This function
		  should generally invoke another thread, or run via an idle
		  handler callback.  During the import it may call <link
		    linkend="API-e-import-status">e_import_status()</link> to
		  report progress.  It must call <link
		    linkend="API-e-import-complete">e_import_complete()</link>
		  once the import is complete, or has failed, or there was no
		  work selected by the user.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>cancel</parameter></term>
	      <listitem>
		<simpara>
		  This optional callback will be invoked if the user activates
		  the cancel button on the import window.  It should try to
		  short-cut further processing where possible.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>name</parameter></term>
	      <listitem>
		<simpara>
		  The short name description of the importer, which will be
		  used in the import type selection dropdown, or next to the
		  application importer widgets.
		</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><parameter>description</parameter></term>
	      <listitem>
		<simpara>
		  A longer description of the importer.  Currently unused.
		</simpara>
	      </listitem>
	    </varlistentry>
	  </variablelist>
	</sect2>
      </sect1>

    </chapter>
  </part>

  <part>
    <title>
      &Evolution; Hook Points.
    </title>
    <partintro>
      <para>
	This section enumerates all of the published hook points and target
	types available in each component in &Evolution;.
      </para>

      <simplesect>
	<title>Table Format</title>
	<informaltable>
	  <tgroup cols="2">
	    <colspec colnum="1" colname="field" colwidth="1*"/>
	    <colspec colnum="2" colname="value" colwidth="4*"/>
	    <tbody>
	      <row>
		<entry>Id</entry>
		<entry>The hook point id.</entry>
	      </row>
	      <row>
		<entry>Target</entry>
		<entry>The target which this hook uses for its context data.
		  Targets are described in a following section.
		</entry>
	      </row>
	      <row>
		<entry>Items</entry>
		<entry>If appropriate and defined, specifies identifying path
		  names of items which make up the hook.  e.g. popup menu
		  items, and configuration pages.  These item specifications
		  allow the plugin writer to position their items
		  appropriately.
		</entry>
	      </row>
	    </tbody>
	  </tgroup>
	</informaltable>
      </simplesect>

    </partintro>
    <chapter id="mail-hooks">
      <title>
	Mail Hooks
      </title>
      <para>
	<emphasis>
	  Need to find out the right docbook to mark-up most of this
	  text.
	</emphasis>
      </para>

      <sect1 id="mail-hooks-popup">
	<title>Popup menus</title>

	<para>
	  The mail popup menu class is
	  <interfacename>org.gnome.evolution.mail.popup:1.0</interfacename>.
	</para>
	<para>
	  The plugin callback data will be the target matching the plugin
	  menu itself, and the callback returns no value.
	</para>

	&em-popups;

	<sect2>
	  <title>Internal popup menus</title>
	  <para>
	    The following popup menus are defined, but they are used with no
	    target, and so provide no useful context if they were to be hooked
	    onto.
	  </para>
	  <para>
	    <interfacename>com.ximian.mail.messagelist.popup.drop</interfacename>
	    is used for the ASK drop type on the message list.
	  </para>
	  <para>
	    <interfacename>com.ximian.mail.storageset.popup.drop</interfacename>
	    is used for the ASK drop type on the folder tree.
	  </para>
	</sect2>

	<sect2>
	  <title>Mail Popup Targets</title>

	  <para>
	    <emphasis>
	      Not sure if this needs to explain the qualifier meanings, or
	      leave it to the in-line comment stuff in the enumeration
	      definition.  Maybe it just needs a direct link to the
	      enumeration.
	    </emphasis>
	  </para>

	  <sect3 id="mail-hooks-popup-EMPopupTargetFolder">
	    <title>Folder Target</title>

	    <para>
	      This target is used to define actions on a folder context.
	      Normally associated with the folder tree.
	    </para>

	    <informaltable>
	      <tgroup cols="2">
		<colspec colnum="1" colname="field" colwidth="1*"/>
		<colspec colnum="2" colname="value" colwidth="4*"/>
		<tbody valign="top">
		  <row>
		    <entry>Name</entry>
		    <entry><constant>folder</constant></entry>
		  </row>
		  <row>
		    <entry>Structure</entry>
		    <entry>
		      <link
			linkend="API-struct--EMPopupTargetFolder">EMPopupTargetFolder</link>
		    </entry>
		  </row>
		  <row>
		    <entry>Qualifiers</entry>
		    <entry>
		      <simplelist>
			<member><constant>folder</constant> = <constant>EM_POPUP_FOLDER_FOLDER</constant></member>
			<member><constant>store</constant> = <constant>EM_POPUP_FOLDER_STORE</constant></member>
			<member><constant>inferiors</constant> = <constant>EM_POPUP_FOLDER_INFERIORS</constant></member>
			<member><constant>delete</constant> = <constant>EM_POPUP_FOLDER_DELETE</constant></member>
			<member><constant>select</constant> = <constant>EM_POPUP_FOLDER_SELECT</constant></member>
		      </simplelist>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	  </sect3>

	  <sect3 id="mail-hooks-popup-EMPopupTargetSelect">
	    <title>Selection Target</title>

	    <para>This target is used to define context for actions associated
	      with a selection of mail messages from a specific folder.</para>

	    <informaltable>
	      <tgroup cols="2">
		<colspec colnum="1" colname="field" colwidth="1*"/>
		<colspec colnum="2" colname="value" colwidth="4*"/>
		<tbody valign="top">
		  <row>
		    <entry>Name</entry>
		    <entry><constant>select</constant></entry>
		  </row>
		  <row>
		    <entry>Structure</entry>
		    <entry>
		      <link
			linkend="API-struct--EMPopupTargetSelect">EMPopupTargetSelect</link>
		    </entry>
		  </row>
		  <row>
		    <entry>Qualifiers</entry>
		    <entry>
		      <simplelist>
			<member><constant>one</constant> = <constant>EM_POPUP_SELECT_ONE</constant></member>
			<member><constant>many</constant> = <constant>EM_POPUP_SELECT_MANY</constant></member>
			<member><constant>mark_read</constant> = <constant>EM_POPUP_SELECT_MARK_READ</constant></member>
			<member><constant>mark_unread</constant> = <constant>EM_POPUP_SELECT_MARK_UNREAD</constant></member>
			<member><constant>delete</constant> = <constant>EM_POPUP_SELECT_DELETE</constant></member>
			<member><constant>undelete</constant> = <constant>EM_POPUP_SELECT_UNDELETE</constant></member>
			<member><constant>mailing_list</constant> = <constant>EM_POPUP_SELECT_MAILING_LIST</constant></member>
			<member><constant>resend</constant> = <constant>EM_POPUP_SELECT_EDIT</constant></member>
			<member><constant>mark_important</constant> = <constant>EM_POPUP_SELECT_MARK_IMPORTANT</constant></member>
			<member><constant>mark_unimportant</constant> = <constant>EM_POPUP_SELECT_MARK_UNIMPORTANT</constant></member>
			<member><constant>flag_followup</constant> = <constant>EM_POPUP_SELECT_FLAG_FOLLOWUP</constant></member>
			<member><constant>flag_completed</constant> = <constant>EM_POPUP_SELECT_FLAG_COMPLETED</constant></member>
			<member><constant>flag_clear</constant> = <constant>EM_POPUP_SELECT_FLAG_CLEAR</constant></member>
			<member><constant>add_sender</constant> = <constant>EM_POPUP_SELECT_ADD_SENDER</constant></member>
			<member><constant>mark_junk</constant> = <constant>EM_POPUP_SELECT_MARK_JUNK</constant></member>
			<member><constant>mark_nojunk</constant> = <constant>EM_POPUP_SELECT_MARK_NOJUNK</constant></member>
			<member><constant>folder</constant> = <constant>EM_POPUP_SELECT_FOLDER</constant></member>
		      </simplelist>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	  </sect3>

	  <sect3 id="mail-hooks-popup-EMPopupTargetURI">
	    <title>URI Target</title>

	    <para>This target defines context for operations on a URI, normally
	      displayed inline somewhere in the message view.</para>

	    <informaltable>
	      <tgroup cols="2">
		<colspec colnum="1" colname="field" colwidth="1*"/>
		<colspec colnum="2" colname="value" colwidth="4*"/>
		<tbody valign="top">
		  <row>
		    <entry>Name</entry>
		    <entry><constant>uri</constant></entry>
		  </row>
		  <row>
		    <entry>Structure</entry>
		    <entry><link
			linkend="API-struct--EMPopupTargetURI">EMPopupTargetURI</link></entry>
		  </row>
		  <row>
		    <entry>Qualifiers</entry>
		    <entry>
		      <simplelist>
			<member><constant>http</constant> = <constant>EM_POPUP_URI_HTTP</constant></member>
			<member><constant>mailto</constant> = <constant>EM_POPUP_URI_MAILTO</constant></member>
			<member><constant>notmailto</constant> = <constant>EM_POPUP_URI_NOT_MAILTO</constant></member>
		      </simplelist>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	  </sect3>

	  <sect3 id="mail-hooks-popup-EMPopupTargetPart">
	    <title>Message Part Target</title>

	    <para>This target defines context for operations on messages, or
	      individual message parts.  The same target is used for inline
	      images or other content which can be encapsulated in a MIME part
	      (i.e. anything).</para>

	    <informaltable>
	      <tgroup cols="2">
		<colspec colnum="1" colname="field" colwidth="1*"/>
		<colspec colnum="2" colname="value" colwidth="4*"/>
		<tbody valign="top">
		  <row>
		    <entry>Name</entry>
		    <entry><constant>part</constant></entry>
		  </row>
		  <row>
		    <entry>Structure</entry>
		    <entry><link
			linkend="API-struct--EMPopupTargetPart">EMPopupTargetPart</link></entry>
		  </row>
		  <row>
		    <entry>Qualifiers</entry>
		    <entry>
		      <simplelist>
			<member><constant>message</constant> = <constant>EM_POPUP_PART_MESSAGE</constant></member>
			<member><constant>image</constant> = <constant>EM_POPUP_PART_IMAGE</constant></member>
		      </simplelist>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	  </sect3>

	  <sect3 id="mail-hooks-popup-EMPopupTargetAttachments">
	    <title>Attachments Target</title>

	    <para>This target is used to define context for operations on the
	      mail composer attachment bar.</para>

	    <informaltable>
	      <tgroup cols="2">
		<colspec colnum="1" colname="field" colwidth="1*"/>
		<colspec colnum="2" colname="value" colwidth="4*"/>
		<tbody valign="top">
		  <row>
		    <entry>Name</entry>
		    <entry><constant>attachments</constant></entry>
		  </row>
		  <row>
		    <entry>Structure</entry>
		    <entry><link
			linkend="API-struct--EMPopupTargetAttachments">EMPopupTargetAttachments</link></entry>
		  </row>
		  <row>
		    <entry>Qualifiers</entry>
		    <entry>
		      <simplelist>
			<member><constant>one</constant> = <constant>EM_POPUP_ATTACHMENTS_ONE</constant></member>
			<member><constant>many</constant> = <constant>EM_POPUP_ATTACHMENTS_MANY</constant></member>
		      </simplelist>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	  </sect3>

	</sect2>
      </sect1>

      <sect1 id="mail-hooks-menu">
	<title>Main menus</title>

	<para>
	  The mail popup menu class is
	  <interfacename>org.gnome.evolution.mail.bonobomenu:1.0</interfacename>.
	</para>
	<para>
	  The plugin callback data will be the target matching the plugin
	  menu itself, and the callback returns no value.
	</para>

	&em-menus;

	<sect2>
	  <title>Mail Menu Targets</title>

	  <sect3 id="mail-hooks-menu-EMMenuTargetSelect">
	    <title>Message Selection Target</title>

	    <para>This target is used to define context for operations on a
	      selection of messages in the view's message list.</para>

	    <informaltable>
	      <tgroup cols="2">
		<colspec colnum="1" colname="field" colwidth="1*"/>
		<colspec colnum="2" colname="value" colwidth="4*"/>
		<tbody valign="top">
		  <row>
		    <entry>Name</entry>
		    <entry><constant>select</constant></entry>
		  </row>
		  <row>
		    <entry>Structure</entry>
		    <entry>
		      <link
			linkend="API-struct--EMMenuTargeSelect">EMMenuTargetSelect</link>
		    </entry>
		  </row>
		  <row>
		    <entry>Qualifiers</entry>
		    <entry>
		      <simplelist>
			<member><constant>one</constant> = <constant>EM_MENU_SELECT_ONE</constant></member>
			<member><constant>many</constant> = <constant>EM_MENU_SELECT_MANY</constant></member>
			<member><constant>mark_read</constant> = <constant>EM_MENU_SELECT_MARK_READ</constant></member>
			<member><constant>mark_unread</constant> = <constant>EM_MENU_SELECT_MARK_UNREAD</constant></member>
			<member><constant>delete</constant> = <constant>EM_MENU_SELECT_DELETE</constant></member>
			<member><constant>undelete</constant> = <constant>EM_MENU_SELECT_UNDELETE</constant></member>
			<member><constant>mailing_list</constant> = <constant>EM_MENU_SELECT_MAILING_LIST</constant></member>
			<member><constant>resend</constant> = <constant>EM_MENU_SELECT_EDIT</constant></member>
			<member><constant>mark_important</constant> = <constant>EM_MENU_SELECT_MARK_IMPORTANT</constant></member>
			<member><constant>mark_unimportant</constant> = <constant>EM_MENU_SELECT_MARK_UNIMPORTANT</constant></member>
			<member><constant>flag_followup</constant> = <constant>EM_MENU_SELECT_FLAG_FOLLOWUP</constant></member>
			<member><constant>flag_completed</constant> = <constant>EM_MENU_SELECT_FLAG_COMPLETED</constant></member>
			<member><constant>flag_clear</constant> = <constant>EM_MENU_SELECT_FLAG_CLEAR</constant></member>
			<member><constant>add_sender</constant> = <constant>EM_MENU_SELECT_ADD_SENDER</constant></member>
			<member><constant>mark_junk</constant> = <constant>EM_MENU_SELECT_MARK_JUNK</constant></member>
			<member><constant>mark_nojunk</constant> = <constant>EM_MENU_SELECT_MARK_NOJUNK</constant></member>
			<member><constant>folder</constant> = <constant>EM_MENU_SELECT_FOLDER</constant></member>
		      </simplelist>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	  </sect3>
	</sect2>
      </sect1>

      <sect1 id="mail-hooks-config">
	<title>Config Windows and Druids</title>

	<para>
	  The mail config class is
	  <interfacename>org.gnome.evolution.mail.config:1.0</interfacename>.
	</para>

	&em-configs;

	<sect2>
	  <title>Mail Config Targets</title>

	  <sect3 id="mail-hooks-config-EMConfigTargetAccount">
	    <title>Account Target</title>

	    <para>The account target is used for configuring accounts, and so
	      has a pointer to the EAccount being configured.  This is a copy
	      of the actual account object, and is copied to the original once
	      the data is ready to commit.</para>

	    <informaltable>
	      <tgroup cols="2">
		<colspec colnum="1" colname="field" colwidth="1*"/>
		<colspec colnum="2" colname="value" colwidth="4*"/>
		<tbody valign="top">
		  <row>
		    <entry>Name</entry>
		    <entry><constant>account</constant></entry>
		  </row>
		  <row>
		    <entry>Structure</entry>
		    <entry>
		      <link
			linkend="API-struct--EMConfigTargetAccount">EMConfigTargetAccount</link>
		    </entry>
		  </row>
		  <row>
		    <entry>Items</entry>
		    <entry>Define some of the items available and where they fit
		      in the gui</entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	  </sect3>

	  <sect3 id="mail-hooks-config-EMConfigTargetPrefs">
	    <title>Preferences Target</title>

	    <para>The preferences target is used for global preferences.  As
	      such it just contains a pointer to the global configuration store
	      - a GSettings.</para>
	    
	    <informaltable>
	      <tgroup cols="2">
		<colspec colnum="1" colname="field" colwidth="1*"/>
		<colspec colnum="2" colname="value" colwidth="4*"/>
		<tbody valign="top">
		  <row>
		    <entry>Name</entry>
		    <entry><constant>prefs</constant></entry>
		  </row>
		  <row>
		    <entry>Structure</entry>
		    <entry>
		      <link
			linkend="API-struct--EMConfigTargetPrefs">EMConfigTargetPrefs</link>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	  </sect3>
	  
	  <sect3 id="mail-hooks-config-EMConfigTargetFolder">
	    <title>Folder Target</title>

	    <informaltable>
	      <tgroup cols="2">
		<colspec colnum="1" colname="field" colwidth="1*"/>
		<colspec colnum="2" colname="value" colwidth="4*"/>
		<tbody valign="top">
		  <row>
		    <entry>Name</entry>
		    <entry><constant>folder</constant></entry>
		  </row>
		  <row>
		    <entry>Structure</entry>
		    <entry>
		      <link
			linkend="API-struct--EMConfigTargetFolder">EMConfigTargetFolder</link>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	  </sect3>
	  
	</sect2>
      </sect1>

      <sect1 id="mail-hooks-event">
	<title>Events</title>

	<para>
	  The mail event class is
	  <interfacename>org.gnome.evolution.mail.events:1.0</interfacename>.
	</para>

	&em-events;

	<sect2>
	  <title>Mail Event Targets</title>

	  <sect3 id="mail-hooks-event-EMEventTargetFolder">
	    <title>Folder Target</title>
	    
	    <informaltable>
	      <tgroup cols="2">
		<colspec colnum="1" colname="field" colwidth="1*"/>
		<colspec colnum="2" colname="value" colwidth="4*"/>
		<tbody valign="top">
		  <row>
		    <entry>Name</entry>
		    <entry><constant>folder</constant></entry>
		  </row>
		  <row>
		    <entry>Structure</entry>
		    <entry>
		      <link
			linkend="API-struct--EMEventTargetFolder">EMEventTargetFolder</link>
		    </entry>
		  </row>
		  <row>
		    <entry>Qualifiers</entry>
		    <entry>List qualifiers</entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	  </sect3>
	</sect2>
      </sect1>

      <sect1 id="mail-hooks-format">
	<title>Formatters</title>

	<para>
	  The mail formatter hook class is
	  <interfacename>com.novell.evolution.mail.format:1.0</interfacename>.
	</para>

	<para>
	  The mail formatter allows the rendering of attachments to be
	  overridden based on the mime-type of the attachment.  There are
	  additional pseudo-mime-types which can be hooked on to to override
	  some basic functions.  These types are invalid mime-types so cannot
	  occur in received messages.
	</para>

	<informaltable>
	  <tgroup cols="2">
	    <colspec colnum="1" colname="field" colwidth="1*"/>
	    <colspec colnum="2" colname="value" colwidth="4*"/>
	    <tbody valign="top">
	      <row>
		<entry><constant>x-evolution/message/prefix</constant></entry>
		<entry>If it exists, this handler will be called before any
		  other content is output.  This can be used to display global
		  message-information, such as follow-up details.  Normally
		  this handler should chain its call to the parent handler once
		  it is finished.</entry>
	      </row>
	      <row>
		<entry><constant>x-evolution/message/rfc822</constant></entry>
		<entry>This handler is called to output messages, including
		  attached messages.  The default handler will output the
		  user-desired message headers and then render the message
		  content.  It also does some processing to do with secured
		  message validation contexts.  As this is not a simple
		  handler, generally this hook point should only be used to
		  supplement the prefix output where it is desirable to operate
		  on attached messages.
		</entry>
	      </row>
	    </tbody>
	  </tgroup>
	</informaltable>

	<sect2>
	  <title>Base Formatter</title>

	  <para>
	    The EMFormat class is the base class for all formatting types.
	    It should only be used to define compound and complex types which
	    do not rely on outputting any textual information, or rely on any
	    screen or print output differences.
	  </para>

	  <informaltable>
	    <tgroup cols="2">
	      <colspec colnum="1" colname="field" colwidth="1*"/>
	      <colspec colnum="2" colname="value" colwidth="4*"/>
	      <tbody valign="top">
		<row>
		  <entry>Name</entry>
		  <entry><constant>EMFormat</constant></entry>
		</row>
		<row>
		  <entry>Target</entry>
		  <entry>
		    <link
		      linkend="mail-hooks-format-EMFormatHookTarget">EMFormatHookTarget</link>
		  </entry>
		</row>
	      </tbody>
	    </tgroup>
	  </informaltable>
	</sect2>

	<sect2>
	  <title>HTML Formatter</title>

	  <para>
	    The EMFormatHTML class is the base class for most formatting types
	    which generate HTML output.  It renders output to a GtkHTML
	    object.  It uses a fairly complex multi-thread approach to the
	    formatting to ensure the user-interface is not blocked for
	    processing.  GtkHTML is used in a limited way by this class for
	    HTML parsing and resolution of embedded objects.  Embedded objects
	    and Widgets may not be used from formatters which hook onto this
	    entry point.
	  </para>

	  <informaltable>
	    <tgroup cols="2">
	      <colspec colnum="1" colname="field" colwidth="1*"/>
	      <colspec colnum="2" colname="value" colwidth="4*"/>
	      <tbody valign="top">
		<row>
		  <entry>Name</entry>
		  <entry><constant>EMFormatHTML</constant></entry>
		</row>
		<row>
		  <entry>Target</entry>
		  <entry>
		    <link
		      linkend="mail-hooks-format-EMFormatHookTarget">EMFormatHookTarget</link>
		  </entry>
		</row>
	      </tbody>
	    </tgroup>
	  </informaltable>

	  <para>
	    <emphasis>This section needs a huge amount of
	      explanation, and/or more detail needs to be added to another
	      section about the formatter class</emphasis>
	  </para>
	</sect2>

	<sect2>
	  <title>HTML Display Formatter</title>

	  <para>
	    The EMFormatHTMLDisplay class is a subclass of EMFormatHTML, and is
	    used as a mail display widget.  As such, it has access to all of
	    the facilities of GtkHTML, such as embedded widgets.  Like the
	    EMFormatHTML class, this uses a complex multi-thread architecture.
	  </para>

	  <informaltable>
	    <tgroup cols="2">
	      <colspec colnum="1" colname="field" colwidth="1*"/>
	      <colspec colnum="2" colname="value" colwidth="4*"/>
	      <tbody valign="top">
		<row>
		  <entry>Name</entry>
		  <entry><constant>EMFormatHTMLDisplay</constant></entry>
		</row>
		<row>
		  <entry>Target</entry>
		  <entry>
		    <link
		      linkend="mail-hooks-format-EMFormatHookTarget">EMFormatHookTarget</link>
		  </entry>
		</row>
	      </tbody>
	    </tgroup>
	  </informaltable>

	  <para>
	    <emphasis>This section needs a huge amount of
	      explanation, and/or more detail needs to be added to another
	      section about the formatter class</emphasis>
	  </para>
	</sect2>

	<sect2>
	  <title>HTML Print Formatter</title>

	  <para>
	    The EMFormatHTMLPrint class is a subclass of EMFormatHTML, and is
	    used as a mail printing widget.  It cannot access embedded
	    widgets.  For most purposes you would normally only connect to the
	    EMFormatHTML hook, and generate generic HTML output which could be
	    printed or shown on-screen if it isn't overriden by the display
	    formatter.
	  </para>

	  <informaltable>
	    <tgroup cols="2">
	      <colspec colnum="1" colname="field" colwidth="1*"/>
	      <colspec colnum="2" colname="value" colwidth="4*"/>
	      <tbody valign="top">
		<row>
		  <entry>Name</entry>
		  <entry><constant>EMFormatHTMLPrint</constant></entry>
		</row>
		<row>
		  <entry>Target</entry>
		  <entry>
		    <link
		      linkend="mail-hooks-format-EMFormatHookTarget">EMFormatHookTarget</link>
		  </entry>
		</row>
	      </tbody>
	    </tgroup>
	  </informaltable>

	  <para>
	    <emphasis>This section needs a huge amount of
	      explanation, and/or more detail needs to be added to another
	      section about the formatter class</emphasis>
	  </para>
	</sect2>

	<sect2>
	  <title>Mail Quote Formatter</title>
	  <para>
	    The EMFormatQuote class is a subclass of EMFormat, and is
	    used as generator for quoted mail content and for
	    inline-forwarding.  This formatter converts message objects into
	    a pure HTML stream, which is not parsed directly, but normally fed
	    to the message composer.
	  </para>
	  <informaltable>
	    <tgroup cols="2">
	      <colspec colnum="1" colname="field" colwidth="1*"/>
	      <colspec colnum="2" colname="value" colwidth="4*"/>
	      <tbody valign="top">
		<row>
		  <entry>Name</entry>
		  <entry><constant>EMFormatQuote</constant></entry>
		</row>
		<row>
		  <entry>Target</entry>
		  <entry>
		    <link
		      linkend="mail-hooks-EMFormatHookTarget">EMFormatHookTarget</link>
		  </entry>
		</row>
	      </tbody>
	    </tgroup>
	  </informaltable>
	</sect2>

	<sect2 id="mail-hooks-format-EMFormatHookTarget">
	  <title>Mail Formatter Targets</title>

	  <para>There is only one target for all mail formatters, and it is
	    implied automatically for all formatter hooks.</para>

	  <informaltable>
	    <tgroup cols="2">
	      <colspec colnum="1" colname="field" colwidth="1*"/>
	      <colspec colnum="2" colname="value" colwidth="4*"/>
	      <tbody valign="top">
		<row>
		  <entry>Structure</entry>
		  <entry>
		    <link
		      linkend="API-struct--EMFormatHookTarget">EMFormatHookTarget</link>
		  </entry>
		</row>
		<row>
		  <entry>Flags</entry>
		  <entry>
		    <simplelist>
		      <member><constant>inline</constant> = <constant>EM_FORMAT_HANDLER_INLINE</constant></member>
		      <member><constant>inline_disposition</constant> =
			<constant>EM_FORMAT_HANDLER_INLINE_DISPOSITION</constant></member>
		      </simplelist>
		  </entry>
		</row>
	      </tbody>
	    </tgroup>
	  </informaltable>

	</sect2>
      </sect1>
    </chapter>

    <chapter id="contacts-hooks">
      <title>
	Contacts Hooks
      </title>
      <para>
	Hooks available in the contacts component.
      </para>

      <sect1 id="contacts-hooks-popup">
	<title>Popup menus</title>

	<para>
	  The contacts popup menu class is
	  <interfacename>org.gnome.evolution.addressbook.popup:1.0</interfacename>.
	</para>

	<!-- TODO: define the entity once it exists 
	&eab-popups; -->

	<sect2>
	  <title>Calendar Popup Targets</title>
	  <para>TBD</para>
	</sect2>
      </sect1>
      
      <sect1 id="contacts-hooks-menu">
	<title>Main menus</title>

	<para>
	  The addressbook menu class is
	  <interfacename>org.gnome.evolution.addressbook.bonobomenu:1.0</interfacename>.
	</para>

	<!-- TODO: define the entity once it exists 
	&eab-menus; -->

	<sect2>
	  <title>Contacts Menu Targets</title>
	  <para>TBD</para>
	</sect2>
      </sect1>

      <sect1 id="contacts-hooks-config">
	<title>Config Windows and Druids</title>
	<para>
	  The addressbook config class is
	  <interfacename>org.gnome.evolution.addressbook.config:1.0</interfacename>.
	</para>
	
	<!-- TODO: define the entity once it exists
	&eab-configs; -->
	
	<sect2>
	  <title>Contacts Config Targets</title>
	  <para>TBD</para>
	</sect2>
      </sect1>

      <sect1 id="contacts-hooks-event">
	<title>Events</title>

	<para>
	  None defined.
	</para>
      </sect1>
    </chapter>

    <chapter id="calendar-hooks">
      <title>
	Calendar Hooks
      </title>
      <para>
	Hooks available in the calendar component.
      </para>

      <sect1 id="calendar-hooks-popup">
	<title>Popup menus</title>

	<para>
	  The calendar popup menu class is
	  <interfacename>org.gnome.evolution.calendar.popup:1.0</interfacename>.
	</para>

	&ecal-popups;

	<sect2>
	  <title>Calendar Popup Targets</title>
	  <para>TBD</para>
	</sect2>
      </sect1>
      
      <sect1 id="calendar-hooks-menu">
	<title>Main menus</title>

	<para>
	  The calendar menu class is
	  <interfacename>org.gnome.evolution.calendar.bonobomenu:1.0</interfacename>.
	</para>
	
	<!-- TODO: define the entity once it exists
	&ecal-menus; -->

	<sect2>
	  <title>Calendar Menu Targets</title>
	  <para>TBD</para>
	</sect2>
      </sect1>

      <sect1 id="calendar-hooks-config">
	<title>Config Windows and Druids</title>
	<para>
	  The calendar config class is
	  <interfacename>org.gnome.evolution.calendar.config:1.0</interfacename>.
	</para>

	<!-- TODO: define the entity once it exists
	&ecal-configs; -->
	
	<sect2>
	  <title>Calendar Config Targets</title>
	  <para>TBD</para>
	</sect2>
      </sect1>

      <sect1 id="calendar-hooks-event">
	<title>Events</title>

	<para>
	  None defined.
	</para>
      </sect1>
    </chapter>

    <chapter id="shell-hooks">
      <title>
	Shell Hooks
      </title>

      <sect1 id="shell-hooks-menu">
	<title>Main menus</title>

	<para>
	  The mail menu class is
	  <interfacename>org.gnome.evolution.shell.bonobomenu:1.0</interfacename>.
	</para>
	<para>
	  The plugin callback data will be the target matching the plugin
	  menu itself, and the callback returns no value.
	</para>
	&es-menus;
      </sect1>
      <sect1 id="shell-hooks-event">
	<title>Events</title>

	<para>
	  The shell event class is
	  <interfacename>org.gnome.evolution.shell.events:1.0</interfacename>.
	</para>

	&es-events;
      </sect1>

      <sect1 id="shell-hooks-import">
	<title>Importers</title>

	<para>
	  Importers are currently global to the shell.  The importer class is
	  <interfacename>org.gnome.evolution.import:1.0</interfacename>.
	</para>
	<para>
	  Each plugin callback is passed the target.  Once the target has been
	  passed to get-widget, the same target will be passed to import or
	  cancel.  This allows information to be stored non-globally across
	  invocations by utilising the GData field in the target.
	</para>
	&es-importers;
      </sect1>

    </chapter>

  </part>

  <part id="reference">
    <title>
      Reference
    </title>
    <partintro>
      <para>
	This section of the book is a detailed API reference of the
	objects and methods that implement the core plugin system and hooks.
      </para>
      <para>
	It contains the detailed information required for all uses of the
	plugin system. That is, implementors
	of new hook types, application developers providing hook points, and
	plugin developers.
      </para>
    </partintro>
    <chapter id="REF-EPlugin">
      <title>
	EPlugin
      </title>
      <para>
	The EPlugin object manages the loading and invocation of physical
	plugin definitions and plugin binaries.  The base EPlugin class is an
	abstract class which loads plugin definitons, resolving hooks, and
	provides an api for invoking callbacks.
      </para>
      <para>
	The EPluginLib object is a concrete derived class of EPlugin which
	handles loading shared libraries using the GModule interface.
      </para>
      &e-plugin-reference;
    </chapter>

    <chapter>
      <title>
	EPopup
      </title>
      <para>
	The EPopup object manages a single popup menu.  It is used to
	application code as a convenience function for building dynamic popup
	menus based on a specific context.
      </para>
      <para>
	The EPopupHook object is loaded by
	the &EPlugin; system, and is used to provide dynamic extension to the
	application context menus.
      </para>
      &e-popup-reference;

      <!-- this looks like bum here, not sure where else to put it though -->
      &em-popup-reference;
    </chapter>

    <chapter>
      <title>
	EMenu
      </title>
      <para>
	The EMenu object manages the menus for a given view or component.  It
	is used by application code to allow the plugin system an entry point
	to current application view.  It may also be used by the application as
	a convenience function to dynamically alter the menu system based on
	user context.
      </para>
      <para>
	The EMenuHook object is loaded by the &EPlugin; system, and is used to
	provide dynamic extension to the application menus.
      </para>
      &e-menu-reference;
    </chapter>

    <chapter>
      <title>
	EConfig
      </title>
      <para>
	The EConfig object manages the building of dynamic configuration pages
	to configure specific application objects.  The same basic object can
	be used to fully drive a wizard-like druid object, or to drive a
	note-book of configuration options.  It is used by application code to
	provide the core controller in a model-view-controller implementation
	of a UI window.
      </para>
      <para>
	The EConfigHook object is loaded by the &EPlugin; system, and is used hook
	in additional configuration items into configuration windows or druids
	dynamically.
      </para>
      &e-config-reference;
    </chapter>

    <chapter>
      <title>
	EEvent
      </title>
      <para>
	The EEvent object manages broadcast of events for a given component or
	application.  It is used by application code to provide the plugin
	system with an entry point for user and system state events.
      </para>
      <para>
	The EEventHook object is loaded by the &EPlugin; system, and is used hook
	event listeners into dynamically loaded event handlers.
      </para>
      &e-event-reference;
    </chapter>

    <chapter>
      <title>
	EMFormat
      </title>
      <para>
	The EMFormat object drives the formatting of MIME message content for
	display, print, and replying.  EMFormatHTML is an implementation of
	EMFormat which writes its output to a GtkHTML instance.
      </para>
      <para>
	The EMFormatHook object is loaded by the &EPlugin; system, and is used hook
	event listeners into dynamically loaded event handlers.
      </para>
      &em-format-reference;
    </chapter>

    <chapter>
      <title>
	EImport
      </title>
      <para>
	The EImport object is used to hold a list of EImportImporter
	structures, which are used to drive the importer window.
      </para>
      &e-import-reference;
    </chapter>
  </part>

</book>