          while test body
               The while command evaluates test as an  expression  (in
               the  same  way  that expr evaluates its argument).  The
               value of the expression must be numeric; if it is  non-
               zero  then  body  is  executed by passing it to the Tcl
               interpreter.  Once body has been executed then test  is
               evaluated   again,   and   the  process  repeats  until
               eventually test evaluates  to  a  zero  numeric  value.
               Continue  commands  may  be  executed  inside  body  to
               terminate the current iteration of the loop, and  break
               commands may be executed inside body to cause immediate
               termination of the while command.   The  while  command
               always returns an empty string.
