What is ETag and how does it works?

An ETag is an opaque identifier assigned by a web server to a specific version of a resource found at an URL. If the resource content at that URL ever changes, a new and different ETag is assigned.



In typical usage, when an URL is retrieved the web server will return the resource along with its corresponding ETag value, which is placed in an HTTP “ETag” field.

What is the process of working in these ETags?

Thank you.