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tag
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... A protocol element (e.g., an entity tag or a Last-Modified time)
that is used to find out whether a cache entry is an equivalent
...
... Language Tags ...
...
A language tag identifies a natural language spoken, written, or
otherwise conveyed by human beings for communication of information
...
... languages are explicitly excluded.
HTTP uses language tags within the Accept-Language and Content-
Language ...
... The syntax and registry of HTTP language tags is the same as that
defined by RFC 1766(-> 3282draft | 3066(-> 4647 | 4646)) [1 ...
... defined by RFC 1766(-> 3282draft | 3066(-> 4647 | 4646)) [1]. In summary, a language tag is composed of 1
or more parts: A primary language tag and a possibly empty series of
...
... 1]. In summary, a language tag is composed of 1
or more parts: A primary language tag and a possibly empty series of
subtags:
...
... subtag = 1*8ALPHA
Whitespace is not allowed within the tag and all tags are case-
insensitive. The name space ...
...
Whitespace is not allowed within the tag and all tags are case-
insensitive. The name space of language tags ...
... tags are case-
insensitive. The name space of language tags is administered by the
IANA. Example tags ...
... language tags is administered by the
IANA. Example tags include:
en, en-US, en-cockney, i-cherokee, x-pig-latin
...
... en, en-US, en-cockney, i-cherokee, x-pig-latin
where any two-letter primary-tag is an ISO 639 language abbreviation
...
... ISO 3166 country code. (The
last three tags above are not registered tags; all but the last are
examples of tags ...
... country code. (The
last three tags above are not registered tags; all but the last are
examples of tags which could be registered in future.)
...
... tags above are not registered tags; all but the last are
examples of tags which could be registered in future.)
...
...
Entity tags are used for comparing two or more entities from the same
requested resource. HTTP/1.1 uses entity ...
... requested resource. HTTP/1.1 uses entity tags in the ETag (section
14.20), If-Match (section 14.25), If-None-Match (section 14.26), and
If-Range ...
... cache validators is in section 13.3.3. An
entity tag consists of an opaque quoted string, possibly prefixed by
a weakness indicator.
...
...
A "strong entity tag" may be shared by two entities of a resource
only if they are equivalent by octet equality.
...
...
A "weak entity tag," indicated by the "W/" prefix, may be shared by
two entities of a resource only if the entities are equivalent and
...
...
An entity tag MUST be unique across all versions of all entities
associated with a particular resource. A given entity ...
... versions of all entities
associated with a particular resource. A given entity tag value may
be used for entities obtained by requests on different URIs without
...
...
Neither the entity tag nor the expiration value can impose an
ordering on responses, since it is possible that a later response
intentionally carries an earlier expiration time. However, the
...
...
Entity tags are normally "strong validators," but the protocol
provides a mechanism to tag an entity ...
... Entity tags are normally "strong validators," but the protocol
provides a mechanism to tag an entity tag as "weak." One can think of
...
... provides a mechanism to tag an entity tag as "weak." One can think of
a strong validator as one that changes whenever the bits of an entity ...
...
An entity tag is strong unless it is explicitly tagged as weak.
Section 3.11 gives the syntax for entity tags ...
... tag is strong unless it is explicitly tagged as weak.
Section 3.11 gives the syntax for entity tags.
A Last-Modified time, when used as a validator in a request, is
...
...
o SHOULD send an entity tag validator unless it is not feasible to
generate one.
o MAY send a weak entity ...
... entity tag instead of a strong entity tag, if
performance considerations support the use of weak entity ...
... performance considerations support the use of weak entity tags, or
if it is unfeasible to send a strong entity tag ...
... tags, or
if it is unfeasible to send a strong entity tag.
o SHOULD send a Last-Modified value if it is feasible to send one,
unless the risk of a breakdown in semantic ...
... HTTP/1.1 origin server
is to send both a strong entity tag and a Last-Modified value.
In order to be legal, a strong entity ...
...
In order to be legal, a strong entity tag MUST change whenever the
associated entity value changes in any way. A weak entity ...
... associated entity value changes in any way. A weak entity tag SHOULD
change whenever the associated entity changes in a semantically
...
... Note: in order to provide semantically transparent caching, an
origin server must avoid reusing a specific strong entity tag value
for two different entities, or reusing a specific weak entity tag ...
... tag value
for two different entities, or reusing a specific weak entity tag
value for two semantically different entities. Cache entries may
...
... tag has been provided by the origin server, MUST
use that entity tag in any cache-conditional request (using
If-Match or If-None-Match).
...
... provide a way to disable this, in case of difficulty.
o If both an entity tag and a Last-Modified value have been
provided by the origin server, SHOULD use both validators in
cache ...
... cache entry. This is only an issue when the
request contains both an entity tag and a last-modified-date
validator (If-Modified-Since or If-Unmodified-Since).
...
... clients and caches will ignore entity tags. Generally,
last-modified values received or used by these systems will support
transparent and efficient caching, and so HTTP/1.1 ...
...
If an entity tag was assigned to the representation, the forwarded
request SHOULD be conditional and include the entity tags ...
... tag was assigned to the representation, the forwarded
request SHOULD be conditional and include the entity tags in an If-
None-Match header field from all its cache ...
... cache which entry is appropriate. If the
entity-tag of the new response matches that of an existing entry, the
new response SHOULD be used to update ...
... to the origin server in a conditional request and the server responds
with 304 (Not Modified), including an entity tag or Content-Location
that indicates which entity ...
... for the associated entity, its entity-tag SHOULD NOT be included in
the If-None-Match header unless the request is for a range ...
... URI, whose entity-tag differs from that of the existing entry, and
whose Date is more recent than that of the existing entry, the
existing entry SHOULD NOT be returned in response to future requests,
...
... language-range matches a language-tag if
it exactly equals the tag, or if it exactly equals a prefix ...
... tag, or if it exactly equals a prefix of the
tag such that the first tag character following the prefix is "-".
...
... prefix of the
tag such that the first tag character following the prefix is "-".
The special range ...
... range "*", if present in the Accept-Language field,
matches every tag not matched by any other range present in the
Accept-Language ...
... prefix matching rule does not imply that
language tags are assigned to languages in such a way that it is
always true that if a user understands a language ...
... always true that if a user understands a language with a certain
tag, then this user will also understand all languages with tags
...
... tag, then this user will also understand all languages with tags
for which this tag is a prefix ...
... The language quality factor assigned to a language-tag by the
Accept-Language field is the quality value of the longest language ...
... language-
range in the field matches the tag, the language quality factor
assigned is 0. If no Accept-Language ...
... tag
Language tags are defined in section 3.10. The primary purpose of
Content-Language is to allow a user to identify and differentiate
...
... entity. The headers used with entity tags are described in
sections 14.20, 14.25, 14.26 and 14.43. The entity tag ...
... tags are described in
sections 14.20, 14.25, 14.26 and 14.43. The entity tag may be used
for comparison with other entities from the same resource (see
...
... obtained from the resource can verify that one of those entities is
current by including a list of their associated entity tags in the
If-Match header field. The purpose of this feature is to allow
...
... entity tags match the entity tag of the entity that
would have been returned in the response to a similar GET request
...
... comparison function (see section 3.11)
to compare the entity tags in If-Match.
If none of the entity ...
...
If none of the entity tags match, or if "*" is given and no current
entity exists, the server MUST NOT perform the requested method ...
... applied if the entity corresponding to the If-Match value (a single
entity tag) is no longer a representation of that resource. This
allows the user to indicate that they do not wish the request to be
successful if the resource has been changed without their knowledge.
...
... obtained from the resource can verify that none of those entities is
current by including a list of their associated entity tags in the
If-None-Match header field. The purpose of this feature is to allow
...
... entity tags match the entity tag of the entity that
would have been returned in the response to a similar GET request
...
...
See section 13.3.3 for rules on how to determine if two entity tags
match. The weak comparison function can only be used with GET or HEAD
...
...
If none of the entity tags match, or if "*" is given and no current
entity exists, then the server MAY perform the requested method ...
... If the client has no entity tag for an entity, but does have a Last-
Modified date, it may use that date in a If-Range ...
... valid HTTP-date and any form of entity-tag
by examining no more than two characters.) The If-Range header ...
... header matches the current
entity tag for the entity, then the server should provide the
specified sub-range ...
... entity using a 206 (Partial content)
response. If the entity tag does not match, then the server should
return the entire entity using a 200 (OK) response.
...
... Alvestrand, H., "Tags for the identification of languages", RFC 1766(-> 3282draft | 3066(-> 4647 | 4646)), UNINETT, March 1995. ...
... entity-header field defines the version tag
associated with a rendition of an evolving entity. Together with the
...
... header field can be used to indicate the
version tag of the resource from which the enclosed entity was
derived before modifications were made by the sender ...