extract information: parametric operetor

I have a problem for extracting text from a document using the operator extract information, when I want to have parametric xpath that contains a call to a macro effect like this:
/ / *[@ class = 'contentheading' and contains (.,. +% {macro}. +)]

But this is not functional %{macro}Since runnig is not replaced by its value

any one can help  ???

thanks you in advance