code: private boolean isJavaXExternal(String className) {
          if (!className.startsWith("javax/")) {
              return false;
          }
  
          if (className.startsWith("javax/xml/")) {
              return true;
          }
  
          int lastSlashPos = className.lastIndexOf('/');
          String packageName = className.substring(0, lastSlashPos);
          ZipEntry ze = jdkZip.getEntry(packageName);
          if (ze != null) {
              return false;
          }
  
          for (String root : knownJDKJavaxPackageRoots) {
              if (className.startsWith(root)) {
                  return false;
              }
          }
  
          return true;
      }
docs: checks to see if this class is a javax.xxxx.Foo class if so, looks to see if the package is at least in the jdk if a whole new package comes into javax
  in rt.jar, this will be missed. Need a better solution here.
  
  @param className
  the slashed class in question
  @return whether it is in the default jdk rt.jar