How to register a wildcard url in Drupal with the hook_menu?

I'm starting to work with Drupal and I'm really confused as how to create a hook_menu function that allows you to register a URL with 1 or 2 different values, that can be hidden and not displayed in the breadcrumbs.

Any help on this would be much appreciated. Even an example.

Solution

Not sure about the breadcrumbs bit, but I think you're looking for wildcard (%) and auto-loader wildcard (%mymodule_entity) components in the path.

From the hook_menu() page...

Wildcards within paths also work with integer substitution. For example, your module could register path 'my-module/%/edit'. When path 'my-module/foo/edit' is requested, integer 1 will be replaced with 'foo' and passed to the callback function. Note that wildcards may not be used as the first component.

$items['my-module/%/edit'] = array(
  'page callback' => 'mymodule_abc_edit',
  'page arguments' => array(1),
);

Registered paths may also contain special "auto-loader" wildcard components in the form of '%mymodule_abc', where the '%' part means that this path component is a wildcard, and the 'mymodule_abc' part defines the prefix for a load function, which here would be named mymodule_abc_load().

$items['my-module/%mymodule_abc/edit'] = array(
  'page callback' => 'mymodule_abc_edit',
  'page arguments' => array(1),
);