In this example we are showing how to add a custom button to user edit form with its own function submission handler.
When you're creating a module in Drupal 7, most likely you'll end up creating some kind of configuration form for your module. In Drupal 7 the easiest way to do this is through variables.
Using flags on large datasets allows for user customisation. A user can flag nodes, comments, users, and any other type of entity. Some possibilities include bookmarking, flagging friends, flagging important, visited/seen or offensive content.