https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag
The ETag HTTP response header is an identifier for a specific version of a resource. It lets caches be more efficient and save bandwidth, as a web server does not need to resend a full response if the content has not changed. Additionally, etags help prevent simultaneous updates of a resource from overwriting each other Syntax:
ETag: W/"<etag_value>"
Directives:
W/ ( Optional)
'W/' (case-sensitive) indicates that a weak validator is used. Weak etags are easy to generate, but are far less useful for comparisons.
"<etag_value>"
Entity tag uniquely representing the requested resource. They are a string of ASCII characters placed between double quotes, like "675af34563dc-tr34"