The class ``ll.url.URL`` supports many common schemes and one additional special scheme named ``root`` that deserves an explanation.

A ``root`` URL is supposed to be an URL that is relative to a “project” directory instead to a base URL of the document that contains the URL.

Suppose we have the following document with the following base URL:

   >>> from ll import url
   >>> base = url.URL("root:company/it/about/index.html")

Now, if we have the following relative URL in this document:

   >>> url1 = url.URL("images/logos/spam.png")

the combined URL will be:

   >>> base/url1
   URL('root:company/it/about/images/logos/spam.png')

Now it we use this combined URL and interpret it relative to the base URL we get back our original relative URL:

   >>> (base/url1).relative(base)
   URL('images/logos/spam.png')

Let's try a ``root`` URL now:

   >>> url2 = url.URL("root:images/logos/spam.png")

Combining this URL with the base URL gives us the same as ``url2``:

   >>> base/url2
   URL('root:images/logos/spam.png')

But if we interpret this result relative to ``base``, we'll get:

   >>> (base/url2).relative(base)
   URL('../../../images/logos/spam.png')

I.e. this gives us a relative URL that references ``url2`` from ``base`` when both URLs are relative to the same root directory.