http://www.tcl.tk/man/tcl8.5/TkCmd/frame.htm
Jeffrey Hobbs has written, "The whole container/use idea is nice, but was only pushed far enough to enable embedding Tk into Netscape/IE. There are definite problems with handling focus and message passing ..."
So I guess it is up to the Tk community to jump in and improve this capability? Let's use "Combining GUI applications developed with Tk and 'native' Windows toolkits" as a home for such progress.
HaO 2016-09-07: (issue is present with pack and grid and with frame and ttk::frame)
Giving a frame with two children:
pack [frame .f -height 1] pack [entry .f.e1] [entry .f.e2]
When on children is unpacked, the frame resizes to the size required by the other children:
pack forget .f.e1
When the last children is unpacked, the frame does not resize:
pack forget .f.e2
-> The frame keeps the size of the entry widget.
To avoid this effect, there are two solutions on clt (Thread "frame auto resize to 0 if forgetting packed subwidget", date 2016-09-05):
bll: Just pack a dummy frame in the collapsing frame:
pack [frame .f] [frame .f.d] pack [entry .f.e1] [entry .f.e2]
Alexandru Dadalau I use the -height property in order to shrink the frame back after the "pack forget".
pack forget .f.e2 .f configure -height 1
This works without a dummy widget but shows a frame of height 1.