[go-nuts] Newbie: Why is the type Header a map[string][]string instead of map[string]string?

I am just confused why use []string as values and not just string. Why is
this required ?

For example - Say I have a cache-control header then this should be enough
if a string type was used for value and not a slice, then
*Header["cache-control"] = ["max-age=200; public"]*

Am I wrong to conclude that ?

Or should this be the correct way ?
*Header["cache-control"] = ["max-age=200", "public"]*