Textual toolbar - %tt[button_text]
This format code is much the same as %bt, except that the button is not as tall.
Also the width of the button is rounded up to one of a set of standard sizes.
This makes it possible to produce a textual toolbar (using a sequence of %tt
formats) as used, for example, in the standard Windows Help buttons "Contents",
"Search", "Back", etc. When using this format you will probably want to remove
the borders from the window using the no_border option of the %ww format.
The text on a button can be changed dynamically by calling