\definemessageconstant {filecontents}
\startmessages startinterface all library: \setinterfacemessage{filecontents }{title: }{filecontents} \setinterfacemessage{filecontents}{1: } {Overwriting file --} \setinterfacemessage{filecontents}{2: } {Writing file --}\stopmessagesstopinterface
\def\startfilecontents