Using must to cross validate CLI

Hi,
my CLI looks like -

router lisp
site site123
   eid-prefix instance-id 100 1.1.1.0/24 accept-more-specifics 
   eid-prefix instance-id 102 2.2.2.0/24 accept-more-specifics 
   eid-prefix instance-id 103 3.3.3.0/24 accept-more-specifics 
site site345
   eid-prefix instance-id 104 4.4.1.0/24 accept-more-specifics 
   eid-prefix instance-id 106 6.6.2.0/24 accept-more-specifics 
extranet ext1
   eid-record-provider instance-id 103

I need a must statement for CLI “eid-record-provider” which validates if the instance-id being used there is defined under “site”.

I have written something like -

     tailf:cli-diff-dependency "../../../../site/eid-prefix/instance-id/id";
     must "../../../../site[name = current()]/eid-prefix/instance-id[id = current() ]" {
       error-message "% Please configure site before provider instance";   
     }  

I am not sure how i am going to iterate must for all sites?

Thanks

Any pointers please on the “must” statement usage.