Section 5.1.2 uses the term 'vacuous document' but there is no clear definition of this term. 'Vacuous' could mean absence of content or absence of meaning.

The current text in section 5.1.2 is as follows:

If the model/*/document/data element has no child element, it is said to contain a vacuous document. If the model/*/document/base64Data element has a zero-length sequence of octets as its value, it similarly contains a vacuous document. If a model definition document or an instance document is a vacuous document, then an SML-IF consumer MUST treat the document as if it is not part of the interchange set.

I propose the following text (which removes this term entirely):

If the model/*/document/data element has no child element, then an SML-IF consumer MUST treat the document as if it is not part of the interchange set. If the model/*/document/base64Data element has a zero-length sequence of octets as its value, then an SML-IF consumer MUST treat the document as if it is not part of the interchange set.