I have to generate a set of IDs in my XSL-FO file, and have done so. However, I get a complaint from Oxygen that: <fo:block " id="1-2">.... E [Xerces] cvc-datatype-valid.1.2.1: '1' is not a valid value for 'NCName'. My programs seem to work, and I do not understand why I am getting this complaint. I thought digits were valid. What is wrong? Mark