Islandora Auto-complete allows users to define auto-complete URL's to be used in a 
Drupal forms in conjuction with the #autocomplete property of form elements.

HOOK_delete_autocomplete_url($id)

Notifies modules that an autcomplete url is being deleted so they may perform any clean up needed.

HOOK_register_autocomplete_source()

Registers an autocomplete source. Used to load a source settings form from the module.

Returns an array like so,
  array(
    'type' => 'machine readable name of source',
    'label' => 'human readable name of source',
    'module' => 'module anem',
    'form' => array( // Describes where the source form is defined.
      'type' => 'file type',
      'file' => 'file'
    ),
  )

HOOK_form
HOOK_form_validate
HOOK_form_submit

Defines/Validates/Submits the source section of the form, just like any Drupal form.

islandora_autocomplete_url_query_HOOK($id, $query, $index)

In this case the HOOK is equal to the type as returned by the modules implementation of register_autocomplete_source()