Markdown 支持两种标题的语法，Setext 和 atx 形式。Setext 形式是用底线的形式，利用 = （最高阶标题）和 - （第二阶标题），Atx 形式在行首插入 1 到 6 个 # ，对应到标题 1 到 6 阶。
区块引用则使用 email 形式的 '>' 角括号。
A First Level Header
====================
A Second Level Header
---------------------
Now is the time for all good men to come to the aid of their country. This is just a regular paragraph.
The quick brown fox jumped over the lazy dog's back.
### Header 3Lv
> This is a blockquote.
>
> This is the second paragraph in the blockquote.
>
> ## This is an H2 in a blockquote
A First Level Header
Header 1
A Second Level Header
Header 2
Now is the time for all good men to come to the aid of their country. This is just a regular paragraph.
The quick brown fox jumped over the lazy dog's back.
Header 3
This is a blockquote.
This is the second paragraph in the blockquote.
This is an H2 in a blockquote
