billboards, URLs are so common, that it's easy to
    overlook their complexity and power. With hyperlink's
    :class:`URL` type, working with URLs doesn't have to be hard.

    URLs are made of many parts. Most of these parts are officially
    named in `RFC 3986`_ and this diagram may prove handy in identifying
    them::

       foo://user:pass@example.com:8042/over/there?name=ferret#nose
       \_/   \_______/ \_________/ \__/\_________/ \_________/ \__/
        |        |          |        |      |           |        |
      scheme  userinfo     host     port   path       query   fragment

    While :meth:`~URL.from_text` is used for parsing whole URLs, the
    :class:`URL` constructor builds a URL from the individual
    components, like so::

        >>> from hyperlink import URL
        >>> url = URL(scheme=u'https', host=u'example.com', path=[u'hello', u'world'])
        >>> print(url.to_text())
        https://example.com/hello/world

    The constructor runs basic type checks. All strings are expected
    to be decoded (:class:`unicode` in Python 2). All arguments are
    optional, defaulting to appropriately empty values. A full list of
    constructor arguments is below.

    Args:
       scheme (unicode): The text name of the scheme.
       host (unicode): The host portion of the network location
       port (int): The port part of the network location. If
          ``None`` or no port is passed, the port will default to
          the default port of the scheme, if it is known. See the
          ``SCHEME_PORT_MAP`` and :func:`register_default_port`
          for more info.
       path (tuple): A tuple of strings representing the
          slash-separated parts of the path.
       query (tuple): The query parameters, as a dictionary or
          as an iterable of key-value pairs.
       fragment (unicode): The fragment part of the URL.
       rooted (bool): Whether or not the path begins with a slash.
       userinfo (unicode): The username or colon-separated
          username:password pair.
       uses_netloc (bool): Indicates whether two slashes appear
          between the scheme and the host (``http://eg.com`` vs
          ``mailto:e@g.com``). Set automatically based on scheme.

    All of these parts are also exposed as read-only attributes of
    URL instances, along with several useful methods.

    .. _RFC 3986: https://tools.ietf.org/html/rfc3986
    .. _RFC 3987: https://tools.ietf.org/html/rfc3987
    Nr