public function addHeader(string $name, string $value) {
        $key = strtolower($name);
        $this->headerNames[$key] = $name;
        $this->headers[$key][] = $value;

        return $this;
    }
public function addHeader(string $name, string $value) {
        $key = strtolower($name);
        $this->headerNames[$key] = $name;
        $this->headers[$key][] = $value;

        return $this;
    }
public function addHeader ( string $ name , string $ value ) { $ key = strtolower ( $ name ) ; $ this -> headerNames [ $ key ] = $ name ; $ this -> headers [ $ key ] [ ] = $ value ; return $ this ; }
Adds a new header with the given value.

If an existing header exists with the given name then the value will be appended to the end of the list.

@param string $name The name of the header.
@param string $value The value of the header.
@return HttpMessage $this Returns `$this` for fluent calls.
Adds a new header with the given value .