Add Metadata section based on infra data structures.

index.html

@@ -3456,6 +3456,73 @@ <h2>
         <h2>
 Metadata Structure
         </h2>
+
+        <p>
+Input and output metadata is often involved during the <a>DID Resolution</a>,
+<a>DID URL Dereferencing</a>, and other DID-related processes. The structure
+used to communicate this metadata MUST be a <a data-cite="INFRA#maps">map</a> of
+properties. Each property name MUST be a <a data-cite="INFRA#string">string</a>.
+Each property value MUST be a <a data-cite="INFRA#string">string</a>,
+<a data-cite="INFRA#maps">map</a>, <a data-cite="INFRA#lists">list</a>,
+<a data-cite="INFRA#boolean">boolean</a>, or  <a data-cite="INFRA#null">null</a>.
+The values within any complex data structures such as maps and lists 
+MUST be one of these data types as well. 
+All metadata property definitions MUST define the value type, including any additional
+formats or restrictions to that value (for example, a string formatted as a date or as a decimal integer).
+It is RECOMMENDED that property definitions use strings for values where possible.
+        </p>
+
+        <p>
+All implementations of functions that use metadata structures as either input or output MUST
+be able to fully represent all data types described here in a deterministic fashion. As inputs and
+outputs using metadata structures are defined in terms of data types and not their serialization,
+the method for representation is internal to the implementation of the function and is out of 
+scope of this specification.
+        </p>
+
+        <p>
+The following example demonstrates a JSON-encoded metadata structure represented
+within a <a href="#did-resolution">DID Resolution process</a>.
+        </p>
+
+        <pre class="example" title="JSON-encoded DID resolution input metadata example">
+{
+  "accept": "application/did+ld+json"
+}
+        </pre>
+
+        <p>
+This example corresponds to a metadata structure of the following format:
+        </p>
+
+        <pre class="example" title="DID resolution input metadata example">
+«[
+  "accept" → "application/did+ld+json"
+]»
+        </pre>
+
+        <p>
+The next example demonstrates a JSON-encoded metadata structure that might be
+used in the return of a <a href="#did-resolution">DID Resolution process</a> if a
+DID was not found.
+        </p>
+
+        <pre class="example" title="JSON-encoded DID resolution output metadata example">
+{
+  "error": "not-found"
+}
+        </pre>        
+
+        <p>
+This example corresponds to a metadata structure of the following format:
+        </p>
+
+        <pre class="example" title="DID resolution output metadata example">
+«[
+  "error" → "not-found"
+]»
+        </pre>
+
     </section>
 
   </section>