Add example and note for ismap, fixes #1303 (#1321)

fixes #1303

Editorial:
* Add example and note for ismap

[I will commit then fix the typo - turns out to be easier that way :)]

Thank you!

sections/semantics-embedded-content.include

@@ -2305,6 +2305,31 @@
   <a>boolean attribute</a>. The attribute must not be specified
   on an element that does not have an ancestor <{a}> element
   with an <{a/href}> attribute.
+
+  <div class="example">
+    In this example the user is asked to identify a person in an image by
+    clicking on it. The server could respond to a click by confirming the
+    correct position or by asking the user to try again.
+
+    <xmp highlight="html">
+      <figure>
+        <a href="solve.html">
+          <img src="zoo.jpg" ismap alt="Animals and people at the zoo, among them Wally with striped clothes">
+        </a>
+        <figcaption>Where’s Wally? Click on him!</figcaption>
+      </figure>
+    </xmp>
+
+    The coordinates where the user clicks are send to the server with the
+    request for the resource referenced by the <{a}> element’s
+    <code>href</code> attribute.
+  </div>
+
+  <p class="note">
+    The definition of the <{a}> element explains how the coordinates of the
+    <code>click</code> event on an <{img}> element with <code>ismap</code>
+    attribute inside an <{a}> element are communicated to the server.
+  </p>
 
   <p class="note">
     The <code>usemap</code> and <code>ismap</code> attributes can result in confusing behavior