Noun
ETag (plural ETags)
Abbreviation of entity tag.
If the client sends an Accept-Encoding: gzip HTTP header for the request and the server provides a gzip-encoded response body, the server might append the characters to the end of the Etag. Source: Internet
You could combine this class with a JavaScript compressor (to improve download speed) and you don't need to care about output changes because ETag is based on sha1 and not on every mktime of each file (it means better server performances). Source: Internet
Because you can’t guarantee a specific file is assigned the same inode number on each web server, the ETag header generated for it will be different from server to server. Source: Internet
If a PHP file can generate different content, e.g. articles from a database, the ETag should be based on the actual content, not the PHP file generating it. Source: Internet
The ETag (entity tag) header field is used to determine if a cached version of the requested resource is identical to the current version of the resource on the server. Source: Internet