widget-attached-popup ?

[Roland Koebler <rk-list koebler com>]

hi,

when you click on a ComboBox, a popup appears, which is "attached" to the
ComboBox. it's the same with i.e. MenuBars.

now: 
how can I create such a "widget-attached-popup" ?
i.e. use a "normal" button, and popup i.e. a treeview when clicking on it.
  
do I have to write my own GtkBin-subclass, or does something like this
already exist ?

thanks,
Roland


p.s.: why I need this:
I don't like popups. I especially hate popups which appear "suddenly", like
a program-windows after a splash-screen (or after a long start-up time), 
error-message-popups or cookie-popups - they steal the focus, clutter the
desktop in several ways, steal keypresses (i.e. type an url in a browser
and press return. while you press return, a cookie/whatever-popup appears
and gets the "return". congratulations: you accepted a cookie/whatever you
didn't want to).
so they simply disturb my work.

"widget-attached-popups" (which do not steal the focus etc.) could solve
this. look at the firefox-Find-"dialog" for a "visual example" (although this
seems to be implemented in an other way).
and I would like something like this in my programs i.e. for error-messages,
i.e. a button on the toolbar which "drops down" a list of all error-messages.