!!! Overview
[{$pagename}] ([Entity-tag]) for [Hypertext Transfer Protocol] as defined in [RFC 2616] [{$pagename}] is useful for checking whether an [Entity] has changed since you last read. 

!! [HTTP Header Field][1]
[{$pagename}] [HTTP Header Field] is defined in [RFC 7232] as, in a [HTTP Response] provides the current [entity-tag] for the selected representation, as determined at the conclusion of handling the request.  An [entity-tag] is an opaque validator for differentiating between multiple representations of the same [resource], regardless of whether those multiple representations are due to [resource] [state] changes over time, content negotiation resulting in multiple representations being valid at the same time, or both.  An [entity-tag] consists of an opaque quoted string, possibly  prefixed by a weakness indicator.

An [entity-tag] can be more reliable for validation than a modification date in situations where it is inconvenient to store modification dates, where the one-second resolution of HTTP date values is not sufficient, or where modification dates are not consistently maintained.
\\[Examples]:
%%prettify 
{{{
ETag: "xyzzy"
ETag: W/"xyzzy"
ETag: ""
}}} 
/%

An entity-tag can be either a weak or strong validator, with strong being the default.  If an origin server provides an entity-tag for a representation and the generation of that entity-tag does not satisfy all of the characteristics of a strong validator ([RFC 7232] Section 2.1), then the origin server MUST mark the entity-tag as weak by prefixing its opaque value with "W/" ([case-sensitive]).
   
!! [SCIM Read Request]
[{$pagename}] may be used in [SCIM Resource Operations]

!! [LDAP]
[{$pagename}] is useful for checking whether an entry has changed since you last read it from the directory. 
[{$pagename}] is often a [Directory Operation] [Virtual Attribute].

!! Attribute Definition
The [{$pagename}] [AttributeTypes] is defined as:
* [OID] of [1.3.6.1.4.1.36733.2.1.1.59] 
* NAME: [{$pagename}]
* DESC: 
* [EQUALITY]: [caseExactMatch]
* [ORDERING]: []
* SYNTAX: [1.3.6.1.4.1.1466.115.121.1.44]
* [SINGLE-VALUE]
* [NO-USER-MODIFICATION]
* USAGE [DirectoryOperation] 
* X-ORIGIN '[OpenDJ] Directory Server'

!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]
----
* [#1] - [ETag|https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag|target='_blank'] - based on information obtained 2018-03-25-