I'm trying to learn specialization by following Eliot Kimber's online tutorial. I've been successful with most of the tutorials, but I'm running into issues with the element domain specialization tutorial. Specifically, I run into problems when I test the specialized element in a topic after adding the reference to the new domain in my DTD file. Oxygen recognizes the specialized element in my test topic since it shows up in the auto-complete list when I begin to enter an element. However, I get the following error after entering the element:
"Invalid format for "class" attribute. Class attribute not specified."
I'm confused by this error message since the class attribute for the specialized element shows up in the attributes window in Oxygen (in this case, "+ topic/keyword xml-d/xmlelem "). I have checked and double-checked my work and I am following everything in the tutorial as written. I know that the tutorial is a bit dated since it was written for DITA 1.2, so maybe there's something missing that changed with DITA 1.3?
Any ideas on why I am getting this error message and what I should be looking for to resolve it?