Smart Stringify Result Marker

     (preprocessor) A result marker of the form <(id)>.  id must correspond
     to the name of a match marker.  A smart stringify result marker
     specifies that the corresponding source text is to be enclosed in quotes
     unless the source text was enclosed in parentheses.  If the matched
     source text is a list, each element of the list is individually
     processed.  If no source text was matched, an empty result is produced.
     The smart stringify result marker is used to implement commands that
     allow extended expressions (a part of a command that may be either an
     unquoted literal or a character expression).