Clarify CR exit criteria requirements for optional features.

index.html

@@ -242,10 +242,10 @@
     <section id='sotd'>
       <p>
 The Working Group is actively seeking implementation feedback for this
-specification. In order to exit the Candidate Recommendation phase, the
-Working Group has set the requirement of at least two independent
-implementations for each mandatory feature in the specification. For details
-on the conformance testing process, see the test suites listed in the
+specification. In order to exit the Candidate Recommendation phase, the Working
+Group has set the requirement of at least two independent implementations for
+each feature, both mandatory and optional, in the specification. For details on
+the conformance testing process, see the test suites listed in the
 <a href="https://w3c.github.io/vc-data-integrity/implementations/">
 implementation report</a>.
       </p>