Whether Squid on cache MISS will pass client revalidation requests
	to the server or tries to fetch new content for caching.
	This is useful while the cache is mostly empty to more quickly
	have the cache populated.

	When set to 'on' (default), Squid will pass all client If-* headers
	to the server.

	When set to 'off' and if the request is cacheable, Squid will
	remove the clients If-Modified-Since and If-None-Match headers from
	the request sent to the server.