Asynchronously writes out the specified name, ensuring it is a valid NmToken according to the W3C XML 1.0 recommendation (http://www.w3.org/TR/1998/REC-xml-19980210#NT-Name).
The task that represents the asynchronous WriteNmToken operation.
This is the asynchronous version of XmlWriter.WriteNmToken(string), with the same functionality. To use this method, you must set the XmlWriterSettings.Async flag to true.