Joomla! Documentation™

A common example of using plugins is to run the content plugins on some text. This is useful if you want to support plugins that usually work on Content from a custom extension. For the latest release of Joomla! 1.5 and newer versions, you can simply use:

$text = JHTML::_('content.prepare', $text);

For early versions of Joomla! 1.5, you need to "spell it out":

$dispatcher =& JDispatcher::getInstance();
$item->text = & your_text_area_item;  
$item->params = clone($params);
JPluginHelper::importPlugin('content'); 
$dispatcher->trigger('onPrepareContent', array (& $item, & $item->params, 0));

You might want to look at core components (for example com_content) for an example.

Also for PHP5.3 compliance please look at the discussion page.