gistfile1.php

/**
 * Implements hook_theme().
 */
function HOOK_theme($existing, $type, $theme, $path) {
  return array(
    'h2' => array(
      'variables' => array('text' => NULL, 'args' => NULL),
    ),
  );
}

/**
 * Theme H2 tags
 */
function theme_h2($variables) {
  return '<h2>' . t($variables['text'], $variables['args']) . '</h2>';
}

// Call the function like this:
theme('h2', 'Summary by database for user @username', array('@username' => $databases['user']->name));