clarification

Broker.md

@@ -29,7 +29,8 @@ especially when some kind of error happens on the server.
 
 The `worker_registry` class is used to store information about workers, their 
 status and the jobs in their queue. It can look up a worker using the headers 
-received with a request. It also uses a basic load balancing algorithm -- the 
+received with a request (a worker is considered suitable if and only if it 
+satisfies all the headers). It also uses a basic load balancing algorithm -- the 
 workers are contained in a queue and whenever one of them receives a job, it is 
 moved to the back, which makes it less likely to receive another job soon.