def start_tag(self, name, attrs=None):
        """Open an XML tag"""
        if not attrs:
            self._write('<%s>' % name)
        else:
            self._write('<' + name)
            for (name, value) in sorted(attrs.items()):
                self._write(
                    ' %s=%s' % (name, quoteattr(scientificformat(value))))
            self._write('>')
        self.indentlevel += 1
Open an XML tag