A [Ttk] [widget] that goes in the south-east corner of a window and allows you to resize the [toplevel] that contains it. Note that on [MacOS X], all windows used to always have something like this by default.

http://www.tcl.tk/man/tcl8.5/TkCmd/ttk_sizegrip.htm documents the widget,
which is used in a [megawidget] or application window to provide a resizing capability.

Formerly called a [Tile] widget.
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