Reverse Proxy Caching using Squid

When Squid is being used as a reverse proxy cache, what happens when a
certain page, which is highly requested, expires in the cache?

Does Squid just let through one request to the web-server (ie the 1st
client that requested the page after it had expired) and return stale
pages to the subsequent requesters, until the page has been
regenerated?

Or does it allow multiple requests through to the web-server when the
page expires?

Rich.