HTTP introduced the Cache-Control header field in RFC 7234 to let servers control the caching of responses and to let clients request a certain behaviour of caches. Answer the following two questions.

a) What is a cache validator and what is the difference between a strong and a weak validator? Why are only pages cacheable that have a cache validator?

b) What is the consequence of the response header:

Cache-Control: max-age=3600, must-revalidate

What is the consequence of the request header:

Cache-Control: max-stale=300