This chapter goes through the process of passing a wildcard variable to a function via an argument from the URL. It creates a MENU_LOCAL_TASK tab on the node which inverts the text to display upside down. It uses a page callback function that is included within a separate file in order to save on how much memory is used.
Check your version
This video covers a topic in Drupal 7 which may or may not be the version you're using. We're keeping this tutorial online as a courtesy to users of Drupal 7, but we consider it archived.