You might encounter a deficiency in the DTDs that in some cases prevents them from adding the @class to an element. DITA2Go adds the @class if possible, and otherwise processes such an element as a <data> element, and writes the following error message to the log file for your project:
No class attribute for element name
To correct this deficiency, for example for <abbreviated-form>:
[ElementClasses]
; Element name = "+ " followed by the full class attribute
; followed by a space.
abbreviated-form = + topic/term abbrev-d/abbreviated-form
Note: The trailing space is required, as is the space following the “+”.
If the DTD does in fact supply @class for an element, as it should, a setting in [ElementClasses] for that element will not override the DTD.