RFC2965规定的cookie实现最小支持

Practical user agent implementations have limits on the number and
size of cookies that they can store. In general, user agents' cookie
support should have no fixed limits. They should strive to store as
many frequently-used cookies as possible. Furthermore, general-use
user agents SHOULD provide each of the following minimum capabilities
individually, although not necessarily simultaneously:

* at least 300 cookies （总体至少300个）

* at least 4096 bytes per cookie (as measured by the characters
that comprise the cookie non-terminal in the syntax description
of the Set-Cookie2 header, and as received in the Set-Cookie2
header) （每个至少支持4k）

* at least 20 cookies per unique host or domain name

(每个域名或者主机至少可以支持20个)
（对cookie实现的最小要求）

User agents created for specific purposes or for limited-capacity
devices SHOULD provide at least 20 cookies of 4096 bytes, to ensure
that the user can interact with a session-based origin server.