Tk::Pane

-sticky => style

If Pane is larger than its requested dimensions, this option may be used to position (or stretch) the slave within its cavity. Style is a string that contains zero or more of the characters n, s, e or w. The string can optionally contains spaces or commas, but they are ignored. Each letter refers to a side (north, south, east, or west) that the slave will "stick" to. If both n and s (or e and w) are specified, the slave will be stretched to fill the entire height (or width) of its cavity.