How do you understand this wordpress plugin triggered within the joomla core "user manager" when a listing of user is displayed?
1. I've already enabled within the plug ins table but it's still no longer working. Things I haven't done?

// no direct access
    defined('_JEXEC') or die('Restricted access');
    // register the handler
    $mainframe->registerEvent('onPrepareContent', 'plgContentUserswi');
    /**
     * 
     * 
     * @param object Content item
     * @param JParameter Content parameters
     * @param int Page number
     */
    function plgContentUserswi(&$row, &$params, $page)
    {
      var_dump($row);
    }

This page consists of their email list of occasions that you could observe having a wordpress plugin. Regrettably it doesn't seem like you should use any one of individuals to attain the thing you need :(

I would be wrong or misuderstood this book here. That does not mean it is wrong but maybe I've get me wrong the interpretation or some earlier explaination which i have skipped. on-page 223 of the book it states the next:

Content
This content plug ins let us modify content products before we display them. The most generally used content event is onPrepareContent. The wedding, always the frst of all of the content occasions to become triggered, can be used to change the written text content. Let us imagine you want to produce a content wordpress plugin that will replace all occurrences of :) having a small smiley face icon. This is the way we're able to implement this:

// no direct access
defined('_JEXEC') or die('Restricted access');
// register the handler
$mainframe->registerEvent('onPrepareContent', 
                          'plgContentSmiley');
/**
 * Replaces :) with a smiley icon.
 * 
 * @param object Content item
 * @param JParameter Content parameters
 * @param int Page number
 */
function plgContentSmiley(&$row, &$params, $page)
{
  $pattern = '/\:\)/';
  $icon = '<img src="plugins/content/smiley.gif" />';
  $row->text = preg_replace($pattern, $icon, $row->text);
}