[Hooks] What is accepted on useEffect's 2nd argument

I assume currently it only do equal (===) comparison, since passing array of array isn't preventing it.

import React, { useState, useEffect } from 'react';

export default () => {
  let [count, setCount] = useState(0);
  let guard = [0, 1, 2];
  useEffect(() => {
    setTimeout(() => {
      setCount(count + 1);
    }, 2000); // delay to prevent lagging
  }, [guard]);
  return <div>{count}</div>;
};

I don't find anything in current documentation. I think it is needed to add accepted types passed into that 2nd argument.

On side note, I wonder what In the future, the second argument might get added automatically by a build-time transformation. phrase means.

从 useEffect 文档的入口和 issue 中的 nested-array 示例开始；确认第二个参数接受什么，以及文档如何描述 dependency 比较。还要解释引用的关于 build-time-transformation 的句子。完成的标准是文档清楚地回答这两个问题，包括该示例的行为。