Drupal：将菜单子项的链接更改为锚点

Question

My goal is to modify the output of a menu so that the submenu links are anchors of the parent item:

<ul class="menu">
  <li>
    <a href="page1">Page 1</a>
    <ul class="submenu">
      <li>
        <a href="page1#section">Section</a>
      </li>
    </ul>
  </li>
</ul>

Because the Drupal GUI doesn't allow anchors in menu items, I need to modify the theme_link() function to change all children:

function MYTHEME_menu_link__menu_block__main_menu(array $variables) {
  $element = $variables['element'];
  $sub_menu = '';

  if ($element['#below']) {

    foreach($element['#below'] as $child) {
      $child['#href'] = str_replace(' ', '-', strtolower(render($child['#title'])));
    }

    $sub_menu = drupal_render($element['#below']);
  }

  $output = l($element['#title'], $element['#href'], $element['#localized_options']);
  return '<li' . drupal_attributes($element['#attributes']) . '>' . $output . $sub_menu . "</li>
";

}

But there are two problems, which are a result of my lack of experience with Drupal functions:

1. The changed href is not being passed to the rendered HTMl.
2. I receive this error for line 8: Warning: Cannot use a scalar value as an array.

What do I need to correct this error, and how can I pass the new href to the menu-children's output link?

EDIT: I should add that I’m using Entity Reference to pull nodes into one super page, and there are three super pages on the site. So using a single-page solution will not work for me.

Answer 1

After much trial and error, I decided to use a non-PHP solution for now. I’m using JavaScript to change the submenu-children's hrefs on page load, which is not necessarily the best solution, but the most feasible right now. It seems like Drupal’s menu functions are better served for modifying the markup and attributes of the menu items, rather than the menu's link attributes. If I return to this issue and come up with a PHP solution, I’ll post it here.

Even though this doesn’t answer my original questions, I’m marking it as the accepted answer because it provides the end result I trying to accomplish.