[wp-hackers] register_setting and unregister_setting

[Stephane Daury]

In regards to http://codex.wordpress.org/Migrating_Plugins_and_Themes_to_2.7#Plugins_need_to_Register_their_Options 
  and http://codex.wordpress.org/Version_2.7#Administration_Manage_Section_API

http://trac.wordpress.org/browser/trunk/wp-admin/includes/plugin.php#L812

Can anyone brief us on what exactly are the register_setting and  
unregister_setting functions are, when/where they'll be required  
exactly and how to use them for our plugins?
Especially since the migration page states that WPMU currently uses  
them.

Thx a bunch,

Stephane