I'm reading the http standard in rfc2616.
Now I want to get the format of If-None-Match. It gives me:
If-None-Match = "If-None-Match" ":" ( "*" | 1#entity-tag )
What is the 1# ? Or dose 1#entity-tag means the exact of ETag ?
It means 1 or more occurrences of "entity-tag".
The syntax is explained in the RFC, in section 2.1, "Augmented BNF":
http://www.w3.org/Protocols/rfc2616/rfc2616-sec2.html#sec2.1
Important note: RFC 2616 is obsolete. It's been superseded by a series of 6 RFCs: 7230, 7231, 7232, 7233, 7234, 7235. See https://www.mnot.net/blog/2014/06/07/rfc2616_is_dead