In this section:
This format code is much the same as %bt (Button), 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 (Textual Toolbar) 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 (Window Style) format.
The text on a button can be changed dynamically by calling CHANGE_BUTTON_TEXT@.