Propertize mode-line contents only for mode-line of selected window?

[Alexis]

Hi all,

i'd like to modify the value of `mode-line-format` such that one 
specific part of it is propertized in a specific way only for the 
mode-line of the currently selected window. Is there some way of 
achieving this via ELisp?  i've not been able to make any progress 
on this with various permutations of `frame-selected-window`, 
`window-buffer`, `current-buffer` etc. ....


Alexis.