code: public void setVisitorDirectory (final File value)
    {
      if (value != null && !value.isAbsolute ())
      {
        throw new IllegalArgumentException ("path is not absolute: " + value);
      }
      this.visitorDirectory = value;
    }
docs: Sets the absolute path to the output directory for the visitor files.
  
  @param value
  The absolute path to the output directory for the generated visitor
  files, may be <code>null</code> to use a sub directory in the output
  directory of the grammar file. If this directory does not exist yet,
  it is created. Note that this path should already include the
  desired package hierarchy because JTB will not append the required
  sub directories automatically.