How to add comments in XML?

There are few ways to add comments in XML:

Method 1:

You can wrap the text with a non-existing processing-instruction as shown below

<book>
<?ignore
  <author>
    <name>john</name>
  </author>
?>
</book>

Method 2:

Use the <!--...--> format to add comments, which is similar to comment in HTML doc:

<!-- 
 <data>
        <data-field1></data-field1>
        <data-field2></data-field2>
        <data-field3></data-field3>
 </data>
-->

Thanks.