Explain schema media type param and Accept

This explains how to use HTTP content negotiation to request
representations that conform to multiple schemas, or conform
to at least one schema out of several.

Author: handrews

jsonschema-core.xml

@@ -2186,7 +2186,8 @@ Content-Type: application/json;
                 </figure>
 
                 <t>
-                    Multiple schemas are whitespace separated:
+                    Multiple schemas are whitespace separated, and indicate that the
+                    instance conforms to all of the listed schemas:
                 </t>
 
                 <figure>
@@ -2198,6 +2199,33 @@ Content-Type: application/json;
                     </artwork>
                 </figure>
 
+                <t>
+                    Media type parameters are also used in HTTP's Accept request header:
+                </t>
+
+                <figure>
+                    <artwork>
+<![CDATA[
+Accept: application/json;
+          schema="http://example.com/qiang http://example.com/li",
+        application/json;
+          schema="http://example.com/kumar"
+]]>
+                    </artwork>
+                </figure>
+
+                <t>
+                    As with Content-Type, multiple schema parameters in the same string
+                    requests an instance that conforms to all of the listed schemas.
+                </t>
+
+                <t>
+                    The Accept header also allows repeating the same media type with
+                    different parameters, which requests that the instance conforms
+                    to one parameter value or the other.  Such an instance can conform
+                    to all separately specified parameters but is not guaranteed to do so.
+                </t>
+
                 <t>
                     <cref>
                         This paragraph assumes that we can register a "schema" link relation.