Outputproperty docu

[Rune Zedeler]

I still don't understand the outputproperty-statement - and the manual 
could be better.

Why does

#(define (make-text-checker text)
   (lambda (grob) (equal? text (ly-get-grob-property grob 'text))))
\score {
  \notes\relative c''' {
    \property Voice.Stem \set #'direction = #1
    \outputproperty #(make-text-checker "m.d.")
      #'extra-offset = #'(-3.5 . -4.5)
    a^2^"m.d." a^2^"m.d."
  }
}


only affect the 1st "m.d." ?

-Rune