Themeing D7 main-menu

A very different approach to your second question: came up with it when I needed a slight color modifications for subdomain colors/style (served from single codebase). Add a server name as class to your body classes (in template.php):

function yourtheme_preprocess_html(&$variables) {
  // Add a class that gives us a domain/server name. A very handy solution in altering domain based style.
  $variables['classes_array'][] = str_replace('.', '-', $_SERVER['SERVER_NAME']);
}

Then you can use a CSS something like that:

a.active, 
.subdomain-name .menu-111 a
{
color: #333;
}

Might be handy in other situations as well of course.

You can customize your theme's some functionality in template.php
Some default functions are there in drupal. If you print the function argument, you will get full page details by array format.
You customize external module field also.
for eg:
We can change the user login text-field label if you written code for this in your theme.

Hi alex,
I am new in the whole durpal thing and I had the same question few days back. Here is the solution I found. Please correct me if I got something wrong.

HYPOTHESIS:

1. I want to override the links__system_main_menu theme
2. I want to do it through a custom module called mymenu

SOLUTION:

1. Create the module folder for the module mymenu and all the necessary files in it.
2. Implement the hook_theme as follows. Probably you will do that in the mymenu.tpl.php:
   

   function mymenu_theme($existing, $type, $theme, $path) {
     return array(
       'links__system_main_menu' => array( //Override the main menu theme
         'variables' => array(),
         'template' => 'links__system_main_menu', //Note that the template name defined here has no .tpl.php extension.
       ),
     );
   }
   

3. Create your custom template for your links in the module folder. In our case the template file will be called links__system_main_menu. Here is a sample template (do not use on a live site.)
   

   <div>
     <ul>
     <?php
       foreach ($links as $link) {
         echo '<li>'.l($link['title'], $link['path'], $link).'</li>';
       }
     ?>
     </ul>
   </div>
   

4. Activate your module, clear the cache and check the results. Remember to clear your cache every time you make changes to your module.

NOTES:

1. In your implementation of hook_theme you may use the function key instead of the template one and write a custom function to return your HTML. e.g.: 'function' => 'your_function_callback'
2. You can probably do all the things above, in the scope of a theme without having to implement a new module, but I don't know the way to do it yet.
3. For the other newcomers to drupal world (like me) out there, I would like to note that hook_theme(http://api.drupal.org/api/drupal/modules--system--system.api.php/functio...) is used to register a theme while theme(http://api.drupal.org/api/drupal/includes--theme.inc/function/theme/7) is used to use a registered theme.

Hi, I am reporting back from the Drupal documentation trenches. ;-)
I found a more elegant solution to your first problem, here it is...

HYPOTHESIS:

1. I want to override the links__system_main_menu theme
2. I want to do it through a custom theme called mytheme

SOLUTION:

1. Create the theme folder for the theme mytheme and all the necessary files in it. And make it default theme.
2. Implement the hook_links__system_main_menu as follows. Probably you will do that in the template.php file in your theme folder.:
   

   function mytheme_links__system_main_menu($variables) {
     $html = "<div>\n";
     $html .= "  <ul>\n";  
     foreach ($variables['links'] as $link) {
       $html .= "<li>".l($link['title'], $link['path'], $link)."</li>";
     }
     $html .= "  </ul>\n";
     $html .= "</div>\n";
   
     return $html;
   }
   

NOTES:

1. It is possible to implement your theme in a template file. To do that you have to implement the hook_theme hook in the teplate.php (see my previous comment for sample code on hook_theme implementation).

I've read all the comments. And after that, I have succeeded.

template.php

function yourtheme_preprocess_page(&$variables){
	// Primary nav.
	$variables['primary_nav'] = FALSE;
	if ($variables['main_menu']) {
		// Build links.
		$variables['primary_nav'] = theme('links__system_main_menu', array('links' => $variables['main_menu']));
	}
}

continue in the same file

function yourtheme_links__system_main_menu(&$variables) {
  $links = '<ul>';
  foreach ($variables['links'] as $link) {
    $links .= "<li>".l($link['title'], $link['href'], $link)."</li><li class='sep'></li>";
  }
 $links .= '</ul>';
 return $links;
}

page.tpl.php or any order

...
<?php print render($primary_nav); ?>
...