header in score block not working

[Federico Bruni]

I need to put the \header block inside the \score block.
Could you please tell me what's wrong in this example (it prints 
nothing in the header)?

Thanks!
Federico


\version "2.13"
\include "english.ly"


firstpiece = \relative c' {
  c d e fs
}


\score {
  \new Staff {
    \firstpiece
  }
  \header {
    title= "First Piece"
    composer = "John Doe"
  }
}