How should I define a MENU_LOCAL_ACTION menu item, and which is the involved page callback? Looking at user_menu() to check the answer for another question, I noticed the function contains the following definition.

  $items['admin/people/create'] = array(
    'title' =&gt; 'Add user', 
    'page arguments' =&gt; array('create'), 
    'access arguments' =&gt; array('administer users'), 
    'type' =&gt; MENU_LOCAL_ACTION,
  );


The page callback is not explicitly defined. 

Reading the definition of MENU_LOCAL_ACTION given in hook_menu(), I read  the following:


  MENU_LOCAL_ACTION: Local actions are menu items that describe actions on the parent item such as adding a new user or block, and are rendered in the action-links list in your theme.


That doesn't explain which is the involved page callback that is called to handle that menu item.

Which is the page callback that is called to handle a MENU_LOCAL_ACTION menu item? Is there any other property that is necessary to define such menu items?
Router items can inherit properties from parent paths.

In this case, the page callback is inherited from the 'admin/people' path:

$items['admin/people'] = array(
  'title' =&gt; 'People', 
  'description' =&gt; 'Manage user accounts, roles, and permissions.', 
  'page callback' =&gt; 'user_admin', 
  'page arguments' =&gt; array('list'), 
  'access arguments' =&gt; array('administer users'), 
  'position' =&gt; 'left', 
  'weight' =&gt; -4, 
  'file' =&gt; 'user.admin.inc',
);


The fact that the menu item is a MENU_LOCAL_ACTION doesn't actually come into it, the same is true of any type of item.

So if you define a router item like this:

$items['mymodule/path'] = array(
  'title' =&gt; 'Something',
  'page callback' =&gt; 'mymodule_page_callback',
  'access callback' =&gt; 'mymodule_access_callback',
);


And then define one like this:

$items['mymodule/path/sub-path'] = array(
  'title' =&gt; 'Something',
  'type' =&gt; MENU_LOCAL_ACTION,
  'access callback' =&gt; 'mymodule_access_callback',
);


The page callback will be inherited from the 'parent' item.