Yesterday, a question tagged #psr7 on Twitter caught my eye: #psr7 Request::getHeader($name) return array of single string instead of strings in #Slim3? cc: @codeguy pic.twitter.com/ifA9hCKAPs @feryardiant (tweet) The image linked provides the following details: When I call $request->getHeader('Accept') for example, I was expected that I'll get something like this: Array( [0] => text/html, [1] =>