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IMPORTANT! Please deactivate before upgrading, then re-activate the plugin.

MANUAL INSTALLATION

Unpack the contents to wp-content/plugins/ so that the files are in a collapsing-archives directory. Now enable the plugin. To use the plugin, change the following here appropriate (most likely sidebar.php):

Change From:

<ul>
     <?php wp_get_archives(); ?>
</ul>

To something of the following:

    <?php
     if( function_exists('collapsArch') ) {
      collapsArch();
     } else {
      echo "<ul>\n";
      wp_get_archives();
      echo "</ul>\n";
     }
    ?>

You can specify options for collapsArch. See options section.

WIDGET INSTALLATION

For those who have widget capabilities, (default in Wordpress 2.3+), installation is easier.

Unzip contents to wp-content/plugins/ so that the files are in a collapsing-archives directory. You must enable the Collapsing Archives plugin, then simply go the Presentation > Widgets section and add the Collapsing Archives Widget.