Applications ( web pages ) in browser environment are referencing each other via direct Window object
reference and by name via several APIs like window.frames, window.open, and target
attribute on FORM or A link.
<embed-page> uses same API to reference other microapplication windows
( instances of <embed-page> ) and parent application ( parent window ).
While the direct reference to window object via window.open assumes the straight ownership relation
( only creator has reference to child and child has back reference to parent ),
the named windows have a "global" in browser scope. Meaning different apps could use same name
( legit or not aside )
to reference another application(window). In JS it is counted a bad practice to use global variables as it
threatens the integrity of application. On application level it threatens even more: cross-application integrity
and user safety.
To solve the issue of global nature of named application window, <embed-page/>
limits the iteration of named apps to child/parent and scoping by target groups defined by parent. This way the
visibility (and referencing by target ) is limited to parent-child tree. The child could see the
parent and only siblings under same target scope.