A custom agenda view for archivable non-project tasks?

[Laurynas Biveinis <laurynas.biveinis@gmail.com>]

Hi -

I am trying to implement the following but I am not really getting
anywhere. I want to have a block in a custom agenda that lists all
"archivable" tasks, where "archivable" means in any of "done" states
and not in a project. In my system projects are subtrees that have
'project' tag associated with them. This tag is non-inheritable and
I'd rather keep it that way.

So I would like to have a way to list all items in a done state where
there is no 'project' tag on it nor in any of its (indirect) parents.

Alternatively listing "archivable" projects too would work (these
would be defined as all subitems in a "done" state - not necessarily
the project itself in a "done" state), as long as its subitems are not
listed, but that sounds more complex.

TIA for any pointers to the right direction,
-- 
Laurynas