Rails - Aug 2014 - What is the question mark inside this regex doing?

I thought the ? matches zero or one occurrence of a pattern. However in 
this example:

def show_regexp(string, pattern)
  match = pattern.match(string)
  if match
    "#{match.pre_match}->#{match[0]}<-#{match.post_match}"
  else
    "no match"
  end
end

a = "The moon is made of cheese"
show_regexp(a, /\s.*?\s/) #=> The-> moon <-is made of cheese

What exactly is the ? doing?

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To view this discussion on the web visit
https://groups.google.com/d/msgid/rubyonrails-talk/8d5efdaa-d690-4a34-8a84-e7c1c3696dd3%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.