> Jean-Francois Moulin <mailto:jean-francois.moulin@hzg.de>
> 13. Juni 2016 um 16:39
> Hi!
>
> I am trying to create a custom reference line with the letter module.
> I would like for instance to display the typical phone and email fields
> and additionaly eg a not yet existing field such as mobile={12345} (or
> foo={bar})
>
> At first I did not manage to have any field displayed at all but the use
> of setupletterlayer as described in
> https://mailman.ntg.nl/pipermail/ntg-context/2013/073560.html helped
> (seems the manual from 2010 is no longer up to date...). Unfortunately
> this writes the reference line with labels only for phone an email but
> not for mobile nor foo, The value of the parameter is writen though, so
> it seems I am half the way.
You have to set a text for the new labels with 
\setuplettertext[en][mobile=Mobile,foo=Foobar].

Wolfgang