'Adjust the given ``uri`` based on the given relative URI.'

def adjust_uri(self, uri, relativeto):

    key = (uri, relativeto)
    if (key in self._uri_cache):
        return self._uri_cache[key]
    if (uri[0] != '/'):
        if (relativeto is not None):
            v = self._uri_cache[key] = posixpath.join(posixpath.dirname(relativeto), uri)
        else:
            v = self._uri_cache[key] = ('/' + uri)
    else:
        v = self._uri_cache[key] = uri
    return v
