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<chapter id="plugin-intro">
    <title>Introducing the Plugin API</title>
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    <!-- jEdit 4.0 Plugin Guide, (C) 2001, 2002 John Gellene          -->
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    <indexterm>
        <primary>Plugin API</primary>
        <secondary>introduction</secondary>
    </indexterm>

    <para>The <firstterm>jEdit Plugin API</firstterm> provides a framework for
    hosting plugin applications without imposing any requirements on the design
    or function of the plugin itself. You could write an application that
    performs spell checking, displays a clock or plays chess and turn it into a
    jEdit plugin. There are currently over 50 released plugins for jEdit. While
    none of them play chess, they perform a wide variety of editing and file
    management tasks.</para>

    <para>A detailed listing of available plugins is available at <ulink
    url="http://plugins.jedit.org">plugins.jedit.org</ulink>. You can also find
    beta versions of new plugins in the <quote>Downloads</quote> area of <ulink
    url="http://community.jedit.org">community.jedit.org</ulink>.</para>

    <para>Using the <quote>Plugin Manager</quote> feature of jEdit, users with
    an Internet connection can check for new or updated plugins and install and
    remove them without leaving jEdit. See <xref linkend="using-plugins" /> for
    details.</para>

    <para>Requirements for <quote>plugging in</quote> to jEdit are as
    follows:</para>

    <itemizedlist>
        <listitem>
            <para>This plugin must supply information about itself, such as its
            name, version, author, and compatibility with versions of
            jEdit.</para>
        </listitem>

        <listitem>
            <para>The plugin must provide for activating, displaying and
            deactivating itself upon direction from jEdit, typically in response
            to user input<footnote>
                    <para>You should test your plugin by loading and unloading
                    it from both the Plugin Manager, as well as the <emphasis
                    role="bold">Activator Plugin</emphasis>.</para>
                </footnote>. Make sure you can continue to use both your plugin
            and the editor after it has been reloaded.</para>
        </listitem>

        <listitem>
            <para>Each Plugin has an ActionSet defined by jEdit, which is added
            to the main ActionContext. The ActionSet is a container for
            EditAction instances. The plugin may define
            <firstterm>actions</firstterm> in a number of ways. One way is
            explicitly, with an action definition file known as
            <literal>actions.xml</literal>. Another is implicitly, by defining
            dockable windows in <literal>dockables.xml</literal>.</para>

            <para>Most EditActions are small blocks of BeanShell code that jEdit
            will perform on behalf of the plugin upon user request. They provide
            the <quote>glue</quote> between user input and specific plugin
            routines.</para>

            <para>By convention, plugins display their available actions in
            submenus of jEdit's <guimenu>Plugins</guimenu> menu; each menu item
            corresponds to an action. Plugin authors do not define specific
            shortcuts - the user can/will assign EditActions to keyboard
            shortcuts, toolbar buttons, or entries in the text area's Context
            menu (right-click menu).</para>
        </listitem>

        <listitem>
            <para>The plugin may, but need not, provide a user interface.</para>

            <para>If the plugin has a visible interface, it can be shown in any
            object derived from one of Java top-level container classes:
            <classname>JWindow</classname>, <classname>JDialog</classname>, or
            <classname>JFrame</classname>. jEdit also provides a dockable window
            API, which allows plugin windows derived from the
            <classname>JComponent</classname> class to be docked into views or
            shown in top-level frames, at the user's request.</para>

            <para>Plugins can also act directly upon jEdit's text area. They can
            add graphical elements to the text display (like error highlighting
            in the case of the <application>ErrorList</application> plugin) or
            decorations surrounding the text area (like the
            <application>JDiff</application> plugin's summary views). These
            plugins are dependent on the JEditTextArea class, which is currently
            getting refactored.</para>
        </listitem>

        <listitem>
            <para>Plugins may provide a range of options that the user can
            modify to alter their configuration.</para>

            <para>If a plugin provides configuration options in accordance with
            the plugin API, jEdit will make them available in the
            <guilabel>Global Options</guilabel> dialog box.</para>
        </listitem>

        <listitem>
            <para>While it is not required, plugins are encouraged to provide
            documentation.</para>
        </listitem>
    </itemizedlist>

    <para>As noted, many of these features are optional; it is possible to write
    a plugin that does not provide actions, configuration options, or dockable
    windows. The majority of plugins, however, provide most of these
    services.</para>

    <sidebar>
        <title>Plugins and different jEdit versions</title>

        <para>As jEdit continues to evolve and improve, elements of the API may
        change with a new jEdit release.</para>

        <para>On occasion an API change will break code used by plugins,
        although efforts are made to maintain or deprecate plugin-related code
        on a transitional basis. While the majority of plugins are unaffected by
        most changes and will continue working, it is a good idea to monitor the
        jEdit change log, and join the <literal>jedit-devel</literal> mailing list, to keep updated on changes and bug reports, so that you will know when your
        plugin needs to be updated.
        </para>
    </sidebar>
</chapter>