Note retargeting usage in Fullscreen

Mostly so I remember it's not just events.

Fixes #620.

dom.bs

@@ -5375,7 +5375,6 @@ method, when invoked, must run these steps:
 </ol>
 
 
-
 <h4 id=interface-domimplementation>Interface {{DOMImplementation}}</h4>
 
 User agents must create a {{DOMImplementation}} object whenever
@@ -5704,6 +5703,9 @@ is an object or one of its <a>shadow-including ancestors</a>.
  <li><p>Set <var>A</var> to <var>A</var>'s <a for=tree>root</a>'s <a for=DocumentFragment>host</a>.
 </ol>
 
+<p class=note>The <a>retargeting</a> algorithm is used by <a lt=dispatch>event dispatch</a> as well
+as other specifications, such as <cite>Fullscreen</cite>. [[FULLSCREEN]]
+
 
 <h3 id=interface-element>Interface {{Element}}</h3>
 
@@ -7258,7 +7260,6 @@ must <a lt="split a Text node">split</a> <a>context object</a> with offset <var>
 <a>contiguous <code>Text</code> nodes</a> of the <a>context object</a>, in <a>tree order</a>.
 
 
-
 <h3 id=interface-cdatasection>Interface {{CDATASection}}</h3>
 
 <pre class=idl>
@@ -7267,7 +7268,6 @@ interface CDATASection : Text {
 };</pre>
 
 
-
 <h3 id=interface-processinginstruction>Interface {{ProcessingInstruction}}</h3>
 
 <pre class=idl>
@@ -7284,7 +7284,6 @@ The <dfn attribute for=ProcessingInstruction>target</dfn>
 attribute must return the <a for=ProcessingInstruction>target</a>.
 
 
-
 <h3 id=interface-comment>Interface {{Comment}}</h3>
 
 <pre class=idl>
@@ -9265,7 +9264,6 @@ steps:
 </ol>
 
 
-
 <h3 id="interface-nodefilter">Interface {{NodeFilter}}</h3>
 
 <pre class=idl>