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hook_pathauto_user() 
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The hook_pathauto_user() delivers these possibilities:
1) you can provide aliases for any tab your module adds to the user page
2) you can provide extra placeholders
3) you can add extra code when a new aliases are created for new/updated/deleted users

The hook_pathauto_user() has these parameters:
1) $op = action (taburls, placeholders, values, insert, update, delete)
2) $edit = in case of user change (insert, update, delete) this is the form (what is submitted) and contains the new username for example
3) $user = in case of user change (insert, update, delete) this is the $user object provided by the user module
4) $placeholders = in case of user change (insert, update, delete) this contains the placeholders for making new aliasses.


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1) you can provide aliases for any tab your module adds to the user page
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These paths will be automatically updated when user changes and when bulkupdate is called, so you don't need to provide indsert, update and delete actions.
A new text box will appear in the admin/settings/pathauto

function module_pathauto_user($op, $edit=NULL, $user=NULL, $placeholders=NULL) {
  switch ($op) {
    case 'taburls':
			// URLS I have added as tabs to the user account
			// return an array like:
			// 				tab URL path (after /user/1) => tab name (the name that gets shown in the tab)
			//          
			$settings = array();
			if (module_exist('tracker')) {
					$settings = array('track'  => 'tracker');
			}
      return $settings;
    default:
      break;
  }
}

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2) you can provide extra placeholders
------------------------------

function module_pathauto_user($op, $edit=NULL, $user=NULL, $placeholders=NULL) {
  switch ($op) {
    case 'placeholders':
      $placeholders = array();
      $placeholders[t('[country]')] = t('Country of the user.');
      return $placeholders;
    case 'values':
      $results = array();
      $results[t('[country]')] = pathauto_cleanstring($edit->country);
      return $results;
    default:
      break;
  }
}

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3) you can add extra code when aliases are created for new/updated/deleted users
------------------------------
Use this when you need user based actions where the source is different then usrs/[uid]

function module_pathauto_user($op, $edit=NULL, $user=NULL, $placeholders=NULL) {
  switch ($op) {
		case 'insert':
    case 'update':
			if (module_exist('blog')) {
        $src = 'blog/'.$user->uid;
        $alias = pathauto_create_alias('blog', $op, $placeholders, $src);
      }
			break;
		case 'delete':
			if (module_exist('blog')) {
        path_set_alias('blog/'.$user->uid);
				// delete the feed !!!!
				path_set_alias('blog/'.$user->uid.'/feed');
      }
    default:
      break;
  }
}