if-modified-since vs if-none-match

Question

What could be the difference between if-modified-since and if-none-match? I have a feeling that if-none-match is used for files whereas if-modified-since is used for pages?<

Answer 1

If-Modified-Since uses a date, while If-None-Match uses an ETag. They can both be used for "pages" (i.e. HTML) and other files.