... the while-loop EXPR [is] re-evaluated after each iteration...

It is, but I was trying to make a (perhaps rather trivial) point with regard to continued execution of the loop body (which I've tried to clarify in the original reply) as exemplified below.

>perl -wMstrict -le
"my @ra = (9, 8, 7);
 ;;
 while (@ra) {
   print 0+@ra, ' in @ra';
   shift @ra;
   print 0+@ra, ' in @ra';
   shift @ra;
   print 0+@ra, ' in @ra';
   shift @ra;
   print 0+@ra, ' in @ra';
   shift @ra;
   print 0+@ra, ' in @ra';
   shift @ra;
   print 0+@ra, ' in @ra';
   }
"
3 in @ra
2 in @ra
1 in @ra
0 in @ra
0 in @ra
0 in @ra
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