Concept glossary
Key terms, each followed across the corpus and — where the sources disagree — across the voices that construe it differently.
MUST / REQUIRED / SHALL
absolute requirement
an absolute requirement of the specification — no conforming implementation may do otherwise
292 passages · 2 readings
SHOULD / RECOMMENDED
strong recommendation
there may be valid reasons to ignore this in particular circumstances, but the full implications must be understood and weighed
152 passages
MAY / OPTIONAL
truly optional
genuinely optional — one implementation may do it, another may not, and both conform; neither side may assume the other's choice
146 passages
safe method
GET, HEAD, OPTIONS, TRACE
a method whose defined semantics are essentially read-only — the client does not request, and cannot be held responsible for, any change on the server
1 passages · 2 readings
idempotent method
GET, HEAD, OPTIONS, TRACE, PUT, DELETE
the intended effect on the server of multiple identical requests is the same as for a single such request
1 passages · 2 readings
cacheable
a response is cacheable if a cache is allowed to store a copy and reuse it for a later request
1 passages · 2 readings
resource
the target of an HTTP request, identified by a URI — anything that can be named
1 passages
representation
information intended to reflect a resource's state, in a format that can be communicated in a message — bytes plus metadata
1 passages
intermediary
proxy, gateway, tunnel
an agent that sits on the request/response chain between user agent and origin server, acting as both a server and a client
1 passages
conditional request
If-Match, If-None-Match, If-Modified-Since
a request carrying a precondition field, which the server evaluates before acting — proceeding only if it passes
1 passages
content negotiation
the mechanism by which client and server agree on which representation of a resource to use
1 passages
authority
the authority component; who speaks for a host
the part of a URI naming who is responsible for the resource (host + optional port), and the question of whether a connection is entitled to answer for it
1 passages · 2 readings