=pod 

- ViewPort - component representing part of a page

- Focus - current page

- Tangent - inner stack of a viewport for holding multiple viewports.

- Stack - Hierarchical collection of viewports defining a page

- Event ?

 The focus stack is a linked list of viewports, from outside
in. Outside being the page level, inner items being the various parts
of the page, which can further be broken down into more viewports. The
stack defines the layers of viewports that make up the entire
page. Each viewport also knows what it's target is, the stack
itself. (target_name)(?)

 ViewPorts can be created/added to or removed from the stack using
push_viewport and pop_viewport. An empty focus stack is created by the
begin action in the UI::RootController. The end action does event
delivery before rendering. The push_viewport method in FocusStack
returns the viewport object that was created.

 Per default, a viewport can only contain one inner viewport, to
contain multiple viewports, you need to create a
tangent. $viewport->create_tangent('name') creates a named tangent
stack for the given viewport, onto which more viewports can be pushed.

 A viewport decides which events are are for it, and which for it's
children, it applies the events to the children first, then to
itself. Thus, the innermost viewports are rendered(?) first. By
default, child events are just any focus tangents owned by that
viewport.

 To render the inner viewport in the template for the current
viewport, use [% window.render_viewport(self.inner) %]. If using
tangents for multiple inner viewports, you can select the tangent
using focus_tangent: [%
window.render_viewport(self.focus_tangent('name').vp_outer %].
 

14:29 <@mst> reaction assigns each viewport a param prefix
14:30 <@mst> so '1-foo-0:bar=baz' means 'find $stack->vps->[1]->tangents->{foo}-
>vps->[0] and call $vp->bar('baz')

- connect_event / connect_control, connect_href ?

- Existing ViewPorts: ListView, Field, ActionForm

=cut