[css-variables] computed value of variables with abutting tokens

What should be alerted here?

   <style>
     :root {
       var-a:a;
       var-b:var(a)b;
     }
   </style>
   <script>
     var cs = getComputedStyle(document.documentElement, "");
     alert(cs.getPropertyValue("var-b"));
   </script>

I take it that the computed value of var-b is a stream of two ident 
tokens, with no white space between.  Should this be represented by 
"a/**/b"?

In nearly all situations it won't matter if we treat the value of var-b 
as having a white space token between the two idents.  But it could 
certainly change the validity of a property, for example:

   :root {
     var-a:1px;
     font-size: calc(1px +var(a));
   }