[Nml-wg] NML XML Schema

Peoples, I started to capture the different example XML instance documents into a reference XML schema but have a number of questions. The first question is the use of id and idRef attributes that appear in the examples. I had assumed these were standard XML attributes, however, the URN values in the example XML are not compatible with the XML ID and IDREF attribute types (":" are not allowed in NCNames). Can I use the XML base anyURI type for this? Thank you, John.