
    + Rethink layout engine so checkbutton works
    + add variable traces for -textvariable, -variable
    + integrate XPTheme patch
    + Implement -default option; default button management.
    + alt theme: focus ring should go around text (in check/radio buttons)
      (maybe we can get away with not doing this...)
    + Implement WorldChanged() proc -- handle font (later color) changes.
    + add 'width' resource to label element

    + add fallback fallback "null" element 
