摘要：和的區別，可以從三個層次上來談。首先看中的說明表示強調，表示更強烈的強調。言簡意賅，表明了和的命名來歷。并且在瀏覽器中，默認用斜體表示，用粗體表示。強調事實，討論的是貓是可愛的動物的事實。這里的使用是為了和其他內容區分開來。

em 和 strong 的區別，可以從三個層次上來談。

首先看 HTML 4.01 中的說明：

EM: Indicates emphasis.
STRONG: Indicates stronger emphasis.

em 表示強調，strong 表示更強烈的強調。言簡意賅，表明了 em 和 strong 的命名來歷。并且在瀏覽器中，em 默認用斜體表示，strong 用粗體表示。這是第一個層次上的區別。

第二個層次上，在 Emphasis in context versus overall highlighting 和 em vs. strong 這兩篇文章中，做了很好的總結：

  
em is for local emphasis. You see? Local emphasis. If you would emphasize a word in speech, use em. strong is for global highlighting.

  When somebody looks at your document, at a glance, certain words and phrases should jump out. These are the words and phrases that make up the gist of the content — the highlights.

em 用來局部強調，strong 則是全局強調。從視覺上考慮，em 的強調是有順序的，閱讀到某處時，才會注意到。strong 的強調則是一種隨意無順序的，看見某文時，立刻就凸顯出來的關鍵詞句。斜體和粗體剛好滿足了這兩種視覺效果，因此也就成了 em 和 strong 的默認樣式。

感覺上面已經解釋得很清楚了？我們再來看看第三個層次上的區別。HTML5 標準中做了詳盡解釋：

  
The em element represents stress emphasis of its contents.

  The placement of emphasis changes the meaning of the sentence.——em

  element
  
  
The strong element represents strong importance, seriousness, or urgency for its contents.
  
  
Importance: The strong element can be used in a heading, caption, or paragraph to distinguish the part that really matters from other parts that might be more detailed, more jovial, or merely boilerplate. (This is distinct from marking up subheadings, for which the hgroup element is appropriate.)
  
  
For example, the first word of the previous paragraph is marked up with strong to distinguish it from the more detailed text in the rest of the paragraph.
  
  
Seriousness: The strong element can be used to mark up a warning or caution notice.
  
  
Urgency: The strong element can be used to denote contents that the

  user needs to see sooner than other parts of the document.
  
  
The relative level of importance of a piece of content is given by its number of ancestor strong elements; each strong element increases the importance of its contents.
  
  
Changing the importance of a piece of text with the strong element does not change the meaning of the sentence.——strong element

em 表示內容的重點（stress emphasis），strong 表示強烈的重要性、嚴重性或內容的緊迫性，strong 不會改變所在句子的語意，em 則會改變所在句子的語義。并且舉了一個非常好的例子：

Cats are cute animals.

強調貓，討論的是哪種動物聰明可愛。

Cats are cute animals.

強調事實，討論的是貓是可愛的動物的事實。

Cats are cute animals.

強調可愛，討論的是貓是否可愛。

Chapter 1: The Praxis

"chapter 1"僅僅是個引用，后面strong里的內容才是章節真正的名字。

Flowers, Bees, and Honey and other things I don"t understand

這里strong的使用是為了和其他內容區分開來。

In this example, the strong element is used to denote the part of the text that the user is intended to read first.
在這個例子里，strong標簽是用來指示用戶優先查看的部分內容。

Welcome to Remy, the reminder system.
Your tasks for today:

 
Turn off the oven.
 
Put out the trash.
 
Do the laundry.