https://www.ietf.org/rfc/rfc2326.txt
4.1 Message Types
See [H4.1]
4.2 Message Headers
See [H4.2]
4.3 Message Body
See [H4.3]
12.12 Content-Encoding
See [H14.12]
常常看到 See [H4.1]
但我一直找不到H4.1，指的是哪裡呀？有人知道嗎？