Define new menu status code to ignore page rendering in index.php

Patch for 6.x in attachment.

I'm not sure how does it apply to 7.x (not familiar with 7.x). But basically there are general changes in router_item(), so I'm not sure if this issue is is valid in 7.x.

Even it doesn't change any rendering in 6.x and pass all the tests?

Ok, so hopefully patch will be committed to Panels to fix that issue in 6.x:
#939040: Panels returns NULL from menu_execute_active_handler()
as workaround of this bug/limitation in Drupal 6.x core.

Panels returns NULL, because of Drupal 6.x core limitation and module are not able to pass additional argument into theme('page') to hide the blocks, because parameters are hard-coded in index.php
See: drupal_common_theme()

    'page' => array(
      'arguments' => array('content' => NULL, 'show_blocks' => TRUE, 'show_messages' => TRUE),
      'template' => 'page',
    ),

Additional arguments are available by following the API, but modules can't use it.

merlinofchaos - October 12, 2010 - 20:55
Status: active » closed (works as designed)
Yes. The only way to set the show_blocks flag to theme('page') is to call it manually. There is no way to tell the menu system to add that flag to theme('page').

It is a perfectly valid workflow to call print theme('page', $show_blocks) and then return NULL to indicate that you have rendered the data yourself.

So I could say it's a kind of bug core 6.x specific, if this sounds for you better. Because if you want to use theme argument (which should be available, as described in API), you have to HACK the code workflow by passing the empty/NULL value (which is not expected), to cheat the Drupal core (index.php). By this HACK you could break functionality of core or other modules, what's happening now, because their can't follow the API.
It's the right way to do that?
Is there any API that if you don't render nothing, return none?
In 7.x & 8.x probably this bug doesn't exists.

If NULL value is expected by Drupal core and it's not a bug, where it's described?
http://drupal.org/node/224333#theme_page
As I can see:

Drupal 6:

function mymodule_page_callback() {
  // Assemble page output here...

  // Return page output for Drupal.
  return $output;
}

$output - Return page output for Drupal.
Doesn't say that you can output NULL.

There is as well following function:

function mymodule_page_callback() {
  // Assemble page output here...

  // Return page output for Drupal.
  return theme('page', $output);
}

Question:
It's the proper way of passing custom arguments into 'page' theme callback?
If yes, it does solve my problem.

I think this menu callback example which I found (if it does work) solves the problem of passing custom arguments into 'page' theme in 6.x core:

function mymodule_page_callback() {
  // Assemble page output here...

  // Return page output for Drupal, hide blocks.
  return theme('page', $output, FALSE);
}

http://drupal.org/node/939040#comment-3572484
Thank you for your help and time.

No, above example duplicate the html code. Example is broken.
http://drupal.org/node/428744#comment-1617886