configuring e-tags

Question

I am using Yslow as a simple speed benchmarking tool and I came across a really confusing concept. The E-tag

So the main problem is : How do I configure E-tags? my grade

Answer 1

wikipedia is the man's best friend:)

http://en.wikipedia.org/wiki/HTTP_ETag

Basically a hash as ShZ said, that should be unique or almost for a file.