When a rule is not defined in a wisent grammar, everythings after a line of code that is not handle is not parsed at all.

reading from http://www.randomsample.de/cedetdocs/doc/wisent/Error-recovery.html#Error-recovery the line
     (stmnt (( error ?; )) ;; on error, skip until ';' is read

seems promising enough but I got no idea how to use it, and I was 
looking for a wisent grammar way to ignore tokens.

does it have anything to do with semantic-lex-default-action ?