Fix overview text on setting processing mode from context.

Author: gkellogg

spec/latest/json-ld-api/index.html

@@ -794,10 +794,10 @@ <h3>Overview</h3>
         in the <a>local context</a> <a>array</a> as follows.</p>
 
       <p class="changed">Unless specified using
-        <a data-link-for="JsonLdOptions">processingMode</a> API option, the first
-        <a>context</a> parsed which is a <a>dictionary</a> determines
-        sets the <a>processing mode</a> and
-        affects the behavior of <a>expansion</a> and <a>compaction</a> algorithms.</p>
+        <a data-link-for="JsonLdOptions">processingMode</a> API option,
+        the <a>processing mode</a> is set using the <code>@version</code> member
+        in a local <a>context</a> and
+        affects the behavior of algorithms including <a>expansion</a> and <a>compaction</a>.</p>
 
       <p>If <a>context</a> is a <a>string</a>, it represents a reference to
         a remote context. We dereference the remote context and replace <a>context</a>