Parameter elements include many different input types. The text type provides a textarea where one could enter raw HTML, but since Joomla! has a built-in method for calling a WYSIWYG editor...why not use it?
<params addpath="path/to/folder/elements"> ... <param type="editor" name="myparam" label="HTML Editor" description="Use the editor" default="HTML Goes Here" /> ... </params>
<?php // Check to ensure this file is within the rest of the framework defined('JPATH_BASE') or die(); class JElementEditor extends JElement { var $_name = 'editor'; function fetchElement($name, $value, &$node, $control_name) { $value = str_replace(' ', "\n", $value); $editor =& JFactory::getEditor(); return $editor->display( $control_name.'['.$name.']', $value, '80%', '400', '40', '15', null ) ; } }