Document the de-facto standard of using "@param ..." to indicate a variable number of function arguments.

Better title.

@jhodghdon:

Are there also other functions that do it a different way?

Scanning for all functions that call func_get_args(), I find:

Some Drupal core functions use the @param ... construct:

1. drupal_array_merge_deep()
2. drupal_register_shutdown_function()
3. DatabaseSchema::prefixNonTable()
4. drupal_form_submit()
5. drupal_get_form()
6. module_invoke()
7. module_invoke_all()
8. DrupalWebTestCase::setUp()

Others have a docblock whose @param section is missing or incomplete:

1. file_download()
2. _field_ui_view_mode_menu_access()
3. file_ajax_upload()
4. image_style_deliver()

One uses @param mixed, which is now deprecated:

1. Archive_Tar::setAttribute()

Most Test case functions, and some class methods have no docblock whatsoever:

1. SelectQuery::hasAllTags()
2. SelectQuery::hasAnyTag()
3. SelectQueryExtender::hasAllTags()
4. SelectQueryExtender::hasAnyTag()
5. FieldTestCase::setUp()
6. FieldAttachTestCase::setUp()
7. FieldUITestCase::setUp()
8. FileFieldTestCase::setUp()
9. AJAXTestCase::setUp()
10. MenuBreadcrumbTestCase::setUp()
11. MenuTrailTestCase::setUp()
12. MenuWebTestCase::setUp()

Or the docblock is a one-line-summary that lacks @param lines:

1. DatabaseConnection_sqlite::sqlFunctionConcat()
2. DatabaseConnection_sqlite::sqlFunctionGreatest()
3. field_test_field_create_field()
4. field_test_field_delete()
5. field_test_field_insert()
6. field_test_field_update()