gtk:text-invisible-char (object)

object -- a gtk:text widget
char -- an unsigned integer with an Unicode character

Accessor of the invisible-char slot of the gtk:text class. The gtk:text-invisible-char function retrieves the character displayed in place of the real characters for entries with visibility set to false. Note that GTK does not compute this value unless it needs it, so the value returned by this function is not very useful unless it has been explicitly set. The (setf gtk:text-invisible-char) function sets the character.

By default, GTK picks the best invisible char available in the current font. If you set the invisible char to 0, then the user will get no feedback at all. There will be no text on the screen as they type.