docs: private static String discoverClassName(ClassLoader tccl) {
          String className = null;
  
          // First services API
          className = getClassNameServices(tccl);
          if (className == null) {
              if (IS_SECURITY_ENABLED) {
                  className = AccessController.doPrivileged(
                                  new PrivilegedAction<String>() {
                                      @Override
                                      public String run() {
                                          return getClassNameJreDir();
                                      }
                                  }
                                  );
              } else {
                  // Second el.properties file
                  className = getClassNameJreDir();
              }
          }
          if (className == null) {
              if (IS_SECURITY_ENABLED) {
                  className = AccessController.doPrivileged(
                                  new PrivilegedAction<String>() {
                                      @Override
                                      public String run() {
                                          return getClassNameSysProp();
                                      }
                                  }
                                  );
              } else {
                  // Third system property
                  className = getClassNameSysProp();
              }
          }
          if (className == null) {
              // Fourth - default
              className = "org.apache.el.ExpressionFactoryImpl";
          }
          return className;
      }