How to edit Drupal core rdf.module functionality Using drupal's core RDF module there is a function (shown below) that add "xml:lang" attibute to tags. What I want to do is to change this functionality so that $variables['attributes_array']['xml:lang'] = 'en'; instead of leaving it blank like in the core module. What would be the best way to achieve this? 

/*
 * Implements MODULE_preprocess_HOOK().
 */  
function rdf_preprocess_username(&amp;$variables) {
  // Because xml:lang is set on the HTML element that wraps the page, the
  // username inherits this language attribute. However, since the username
  // might not be transliterated to the same language that the content is in,
  // we do not want it to inherit the language attribute, so we set the
  // attribute to an empty string.
  if (empty($variables['attributes_array']['xml:lang'])) {
    $variables['attributes_array']['xml:lang'] = '';
  }
}
You can add the following preprocess function to template.php in your custom theme. The RDF module is preprocessing the variables used by the theme_username() function. Your custom theme can also preprocess these same variables and override the values set by the RDF module.

/*
 * Implements THEME_preprocess_HOOK().
 */  
function YOURTHEMENAME_preprocess_username(&amp;$variables) {
  $variables['attributes_array']['xml:lang'] = 'en';
}