Add a section, a subsection and some text to the document.

def fill_document(self):
        """Add a section, a subsection and some text to the document."""
        with self.create(Section('A section')):
            self.append('Some regular text and some ')
            self.append(italic('italic text. '))

            with self.create(Subsection('A subsection')):
                self.append('Also some crazy characters: $&#{}')