Update note from review comments

Author: afs

spec/index.html

@@ -642,9 +642,13 @@ <h3>IRIs</h3>
         if a <a data-cite="rfc3986#section-5.1">base IRI
         can be established</a> [[RFC3986]].</p>
 
-      <p><strong>URI Schemes:</strong> Examples of scheme-specific rules include the
-        <a data-cite="RFC7230#section-2.7.1">scheme rules for HTTP</a> and the
+      <p><strong>URI Schemes:</strong>
+        Implementations are encouraged to enforce the scheme-specific rules of
+        the common schemes, such as the
+        <a data-cite="RFC7230#section-2.7.1">scheme rules for HTTP/HTTPS</a> and the
         <a data-cite="did-core#identifier">DID syntax</a>.
+        Implementations ignore URI scheme rules
+        for schemes they do not recognize. 
       </p>
 
       <p><strong>IRI normalization:</strong>