XRD priority attributes

[Victor Grey <victor@idcommons.org>]

WD 9 states in 2.4.3:

"The processing rules for the priority attribute are common across all 
services in the XRI resolution  framework. They apply whenever there is 
more than one instance of the desired element type in an XRD (if there 
is only one instance, the priority attribute is ignored). The rules 
are:
1.  The client SHOULD select the element instance with the lowest 
numeric value of the  priority attribute. For example, an element with 
priority attribute value of “10” should be  selected before an element 
with a priority attribute value of “11”, and an element with priority 
attribute value of “11” should be selected before an element with a 
priority attribute value of “15”. (Zero is the highest priority 
attribute value.)
2.  If two or more instances of the same element type have identical 
priority attribute values,  or if the priority attribute is not 
present, the client SHOULD select one of the instances at random."

This doesn't cover the case where some of the instances have priority 
attributes and some don't (as in the resolution service example at 
2.1).
I'd suggest this:

2.  If two or more instances of the same element type have identical 
priority attribute values the client SHOULD select one of the instances 
at random.
3. A null priority attribute (i.e. the priority attribute is missing) 
has a lower priority than any numeric priority, and two or more 
instances of the same element type that have null priority attributes 
are considered to have identical priority attribute values.

=vg