docs: public CALC use(Class<? extends Extension> operationClass) {
          if (useExtensions == null)
              useExtensions = new UseExtension();
  
          if (Operator.class.isAssignableFrom(operationClass))
              useExtensions.registerOperator(operationClass.asSubclass(Operator.class));
          if (Function.class.isAssignableFrom(operationClass))
              useExtensions.registerFunction(operationClass.asSubclass(Function.class));
  
          return getThis();
      }