> (posn-area (posn-at-x-y (1- (window-pixel-width)) 0))
 >
 > currently gives 'nil' regardless of whether it's done with a header or
 > tab line and
 >
 > (posn-area (posn-at-x-y
 >          (1- (window-pixel-width))
 >          (1- (window-pixel-height))))
 >
 > gives 'nil' on the mode line.  Only when I remove _both_ fringes and the
 > vertical scroll bar I get the expected results.  This _is_ a bug and we
 > should fix it.

I think the attached patch should fix that modulo some ">=" and "<"
glitches.

martin