Convert name to an XML QName

        e.g. pdf:Producer -> {http://ns.adobe.com/pdf/1.3/}Producer

def _qname(self, name):
        """Convert name to an XML QName

        e.g. pdf:Producer -> {http://ns.adobe.com/pdf/1.3/}Producer
        """
        if isinstance(name, QName):
            return name
        if not isinstance(name, str):
            raise TypeError("{} must be str".format(name))
        if name == '':
            return name
        if name.startswith('{'):
            return name
        prefix, tag = name.split(':', maxsplit=1)
        uri = self.NS[prefix]
        return QName(uri, tag)