注意，我们在箭头标记的前面添加了一个空格，当网页可以浏览的时候，箭头标记与文章标题便分开了。

Notice, we added another space before the arrow to separate it from the post title when the page is generated for viewing.

youdao

So if we want to put that in chemical terms, we want to make sure we put these in brackets here, and remember, this is the resonance arrow, it's not a reaction arrow, it's a resonance arrow, so make sure you mark it up correctly like that.

那么如果我们把它类比到化学中来，我们要确保它们都放在括号里，而且要记住，这是一个表示共振态的箭头，而不是表示化学反应的，它是一个表示共振态的箭头，因此请务必像这样正确地标记它。

麻省理工公开课 - 化学原理课程节选