public function setHeader(string $header, string $content): Headers
    {
        $this->headers[self::processKey($header)] = $content;

        return $this;
    }
public function setHeader(string $header, string $content): Headers
    {
        $this->headers[self::processKey($header)] = $content;

        return $this;
    }
public function setHeader ( string $ header , string $ content ) : Headers { $ this -> headers [ self :: processKey ( $ header ) ] = $ content ; return $ this ; }
Set individual header

@param string $header
@param string $content

@return Headers
Set individual header