What takes precedence: the ETag or Last-Modified HTTP header?

Question

For two subsequent requests, which of the following two headers is given more weight by browsers should one of them change: ETag or Last-Modified?

Answer 1

=! is the correct comparison operator. The client is required to keep the literal string received from the server, as conversions can create small differences. You can not assume that 'newer is better'.

Why? Consider the case where the server operator reverts a bad version of a resource. The reverted version is OLDER - but correct.

The client must use the version currently offered by the server; it can use a cached version only if it is the same. Thus the server must check equality, not 'newer'.