Merge pull request #386 from ktoso/wip-spec-amend-allow-not-refering-rule-ktoso

=spec #384 amend spec to allow not mentioning rule number in exception message

Author: viktorklang

README.md

@@ -183,7 +183,7 @@ public interface Subscription {
 | [:bulb:](#3.7 "3.7 explained") | *The intent of this rule is superseded by [3.5](#3.5).* |
 | <a name="3.8">8</a>       | While the `Subscription` is not cancelled, `Subscription.request(long n)` MUST register the given number of additional elements to be produced to the respective subscriber. |
 | [:bulb:](#3.8 "3.8 explained") | *The intent of this rule is to make sure that `request`-ing is an additive operation, as well as ensuring that a request for elements is delivered to the Publisher.* |
-| <a name="3.9">9</a>       | While the `Subscription` is not cancelled, `Subscription.request(long n)` MUST signal `onError` with a `java.lang.IllegalArgumentException` if the argument is <= 0. The cause message MUST include a reference to this rule and/or quote the full rule. |
+| <a name="3.9">9</a>       | While the `Subscription` is not cancelled, `Subscription.request(long n)` MUST signal `onError` with a `java.lang.IllegalArgumentException` if the argument is <= 0. The cause message SHOULD explain that non-positive request signals are illegal. |
 | [:bulb:](#3.9 "3.9 explained") | *The intent of this rule is to prevent faulty implementations to proceed operation without any exceptions being raised. Requesting a negative or 0 number of elements, since requests are additive, most likely to be the result of an erroneous calculation on the behalf of the Subscriber.* |
 | <a name="3.10">10</a>     | While the `Subscription` is not cancelled, `Subscription.request(long n)` MAY synchronously call `onNext` on this (or other) subscriber(s). |
 | [:bulb:](#3.10 "3.10 explained") | *The intent of this rule is to establish that it is allowed to create synchronous Publishers, i.e. Publishers who execute their logic on the calling thread.* |