code: function Headers (size, type, ttl, enc) {
    if (!(this instanceof Headers)) return new Headers(size, type, ttl, enc)
    if (size) this['Content-Length'] = size
    if (type) this['Content-Type'] = type
    if (!isNaN(ttl)) this['Cache-Control'] = 'max-age=' + ttl
    if (enc) this['Content-Encoding'] = enc
  }
docs: - size the size of the entity-body in decimal number of octets - type the media type of the entity-body - ttl the maximum age in seconds - enc the modifier to the media-type