code: private boolean isPackage( StringBuilder s, int i ) {
      try {
        String maybePackage = s.substring( 0, i );
        if( getPackageMethod().invoke( _module.getModuleClassLoader(), maybePackage ) != null ) {
          return true;
        }
      }
      catch( Exception e ) {
        throw new RuntimeException( e );
      }
      return false;
    }
docs: Short-circuit the case where com.foo.Fred is not a class name, but
  com.foo is a package.  Avoid the expensive test for com.foo$Fred as a an
  inner class (and then com$foo$Fred).
  <p>
  Yes, java supports a package and a class having the same name, but in this case
  we are checking for an inner class of a class having the same name as a package...
  Let's just not support references to those in Gosu in the name of both sanity
  and performance.
  <p>
  Warning this design decision was not vetted through various committees, architect
  round tables, community processes, or guys with beards.