'Produce OPF 1.2 representing the book\'s metadata and structure.
Returns a dictionary in which the keys are MIME types and the values
are tuples of (default) filenames and lxml.etree element structures.'

def to_opf1(self):

    package = etree.Element('package', attrib={'unique-identifier': self.uid.id})
    self.metadata.to_opf1(package)
    self.manifest.to_opf1(package)
    self.spine.to_opf1(package)
    tours = element(package, 'tours')
    tour = element(tours, 'tour', attrib={'id': 'chaptertour', 'title': 'Chapter    Tour'})
    self.toc.to_opf1(tour)
    self.guide.to_opf1(package)
    return {OPF_MIME: ('content.opf', package)}
