How to install new MIME types under Nautilus ?

["725eb0c8ef771c09ee" <zjc99 mails tsinghua edu cn>]

Hi all,

I've got very confused with installing new mime types under Nautilus.
I see many apps installing below similar .keys and .mime files under 
<gnome-prefix>/share/mime-info:
//myapp.mime
text/myapp: 
     ext: tst
 
//myapp.keys
text/myapp:
  open=myapp %f
  edit=myapp %f
  print=myapp %f

But after I do so, launching nautilus, and right clicking a file with .tst
extension, there are only "open", "open in new window", and "open with" submenus
in the popup menu. There are no "edit" or "print" submenus, nor is testapp listed
in the "open with" submenu. So, does Nautilus use the verbs registered in the
.keys file ?

I've also seen some other applications using below .keys file instead:
//myapp.keys
text/myapp:
  icon_filename=myapp-icon.png
  description=MyApp
  default_action_type=application
  default_application_id=myapp
  short_list_application_ids_for_novice_user_level=myapp
  short_list_application_ids_for_intermediate_user_level=myapp
  short_list_application_ids_for_advanced_user_level=myapp

In this way, myapp is listed in the popup "open with" submenu, and could be
launched while double right clicking the file.

But most confusingly, some applications use both the "open", "edit", "print"...
and short_list_application_ids_for_***_*** keys:

//myapp.keys
text/myapp:
  open=myapp %f
  edit=myapp %f
  print=myapp %f
  icon_filename=myapp-icon.png
  description=MyApp
  default_action_type=application
  default_application_id=myapp
  short_list_application_ids_for_novice_user_level=myapp
  short_list_application_ids_for_intermediate_user_level=myapp
  short_list_application_ids_for_advanced_user_level=myapp

So, what exactly is the right approach ? Could the "print", "edit" keys be
registered at all ?

I'm quite confused on this point. Any help and comments are appreciated.
 
Thanks.
Daniel.Z