[Exim] .forward filter

Hi list!

I'm making $HOME/.forward filter file.
I try to tell exim

  if $header_from: contains [not] "@local.dom" then
    [sending nolocaladdress@somedomain]
  endif

In []s are my lameness because i don't know the syntax.
Where can i find a full description about filter scripting?
I have red that is simple language, its ok, but i need a descr.

Thanks
Best regards
Gergely Kodaj