Grammar and normative fixes to proof extension point.

Co-authored-by: Ted Thibodeau Jr <[email protected]>
Co-authored-by: Michael B. Jones <[email protected]>

index.html

@@ -2000,8 +2000,8 @@ <h3>Securing Mechanisms</h3>
         </p>
 
         <p>
-It is expected that securing mechanism specifications other than the ones
-referred to above will be created as necessary. A securing mechanism
+Securing mechanism specifications other than those
+referred to above might also be defined, as necessary. A securing mechanism
 specification:
         </p>
 
@@ -2034,8 +2034,8 @@ <h3>Securing Mechanisms</h3>
         </ul>
 
         <p class="note"
-           title="Choice in securing mechanism is use-case dependent">
-There are multiple acceptable securing mechanisms and this specification does
+           title="Choice of securing mechanism is use-case dependent">
+There are multiple acceptable securing mechanisms, and this specification does
 not mandate any particular securing mechanism for use with
 <a>verifiable credentials</a> or <a>verifiable presentations</a>.
 The Working Group that produced this specification did standardize two
@@ -2053,8 +2053,10 @@ <h3>Securing Mechanisms</h3>
         <h3>Proofs</h3>
 
         <p>
-This specification defines the `proof` property for the expression of
-<a href="#dfn-embedded-proof">embedded proofs</a>.
+This specification defines the `proof` property as an extension point for the
+expression of <a href="#dfn-embedded-proof">embedded proofs</a>.
+It is up to each securing mechanism to specify whether or not to use it, and
+if so, how it is to be used.
         </p>
 
         <dl>
@@ -2078,7 +2080,7 @@ <h3>Proofs</h3>
 
         <p>
 Methods of securing <a>verifiable credentials</a> or
-<a>verifiable presentations</a> that embed a proof in the data model MUST use
+<a>verifiable presentations</a> that embed a proof in the data model MAY use
 the <code>proof</code> <a>property</a>. Methods of securing <a>verifiable
 credentials</a> or <a>verifiable presentations</a> that use an <a>enveloping
 proof</a> MAY use the <code>proof</code> <a>property</a>.
@@ -7093,7 +7095,7 @@ <h2>application/vc+ld+json</h2>
         </p>
 
         <p>
-This media type can be used with credentials secured using an
+This media type can be used for credentials secured using an
 <a>enveloping proof</a>.
         </p>
         <p>
@@ -7154,7 +7156,7 @@ <h2>application/vp+ld+json</h2>
         </p>
 
         <p>
-This media type can be used with presentations secured using an
+This media type can be used for presentations secured using an
 <a>enveloping proof</a>.
         </p>
         <p>