The CDL specification says on P17 that "Value references MUST NOT be placed in an element that has child elements"

But there is no coverage of the policy with respect to other child types, such as comments, text and processing 
instructions

Specifically, are the following valid or not

<user1 cdl:ref="../toplevel"><!-- comment node--></user1>
<user cdl:ref="../toplevel">
       <!-- comment node-->
        And some text
</user>

If they are invalid, the spec must say "no children of any type".

If they are valid, the spec must say what is to be done with the nodes during reference resolution. There is an implicit
 specification in the value resolution process (the nested nodes are dropped).

Test case
org/ggf/cddlm/files/cdl/valid/set_02_references/cddlm-cdl-2005-02-0017.xml.