Clarify that different approaches are allowed for context checks.

Author: msporny

index.html

@@ -4890,8 +4890,9 @@ <h3>Context Validation</h3>
 presentations=] that it will process. Not checking these JSON-LD Context values
 against known good values, and the semantics that they convey, can lead to
 security vulnerabilities. While the algorithm above provides one way of checking
-these values, and one optional way of safely processing unknown values, there
-are other approaches that provide the same protections.
+these values, and one optional way of safely processing unknown values,
+implementers MAY use alternative approaches, or a different ordering of the
+steps, that provide the same protections.
         </p>
 
         <p>