defCan-1

I'm puzzled.  In trying to figure out whether an implementation complies 
with defCan-1, the interop doc says

Check that implementations and APIs of [XMLDSIG] honor the recommendation 
to use [XML-C14N1.1] in section 3.1.1 "Reference Generation" of [XMLDSIG] 

Where is this recommendation made?  It's not in section 3.1.1 of xmldsig. 
And I searched for "recommend" and "should" in the c14n11 spec and didn't 
find a recommendation
that seemed to have anything to do with what the test is testing.

What is being alluded to?

Bruce A Rich
brich at-sign us dot ibm dot com