def readVersion(self):
        """ Read the document version.
        ::
            <designspace format="3">
        """
        ds = self.root.findall("[@format]")[0]
        raw_format = ds.attrib['format']
        try:
            self.documentFormatVersion = int(raw_format)
        except ValueError:
            # as of fontTools >= 3.27 'format' is formatted as a float "4.0"
            self.documentFormatVersion = float(raw_format)
Read the document version.
        ::
            <designspace format="3">