How does \fromproperty work?

[Graham Percival]

In the example below, \fromproperty appears to do nothing.  I see
how it is used in ly/titling-init.ly , and as far as I can tell, I'm 
using
it in the same way below.  What's wrong with this example?


\version "2.7.3"
\header { piece = "foo" }
\markup {
  between
  \fromproperty #'header:title
  after
}