'Create the <spine> element. Must first call :method:`create_manifest`.
`entries`: List of paths'

def create_spine(self, entries):

    entries = map((lambda x: (x if os.path.isabs(x) else os.path.abspath(os.path.join(self.base_path, x)))), entries)
    self.spine = Spine.from_paths(entries, self.manifest)
