You can also add comments to an XML document. Comments go just about anywhere and are ignored  for data processing purposes. Comments are bracketed by the <!– and –> character sequences. The following listing includes three valid comments:

 
<?xml version=”1.0″?><BooksList>

<!– This is an example . –>

<Book ISBN-13=” 978-0545139700” Title = Title>Harry Potter and the Deathly Hallows“>

<Author>J.K. Rowling</Author>

<Price>14.99</Price>

<Available>True</Available>

</Book>

<Book ISBN-13=”978-1451648539” Title=”Steve Jobs”>

<Author>Walter Isaacson</Author>

<Price>17.88</Price>

<Available>False <!– Why isn’t available ? –> </Available>

</Book>

<!– Other books omitted for clarity. –>

</BooksList>
The only place you can’t put a comment is embedded within a start or end tag (as in <myData <!– A comment should not go here –></myData>).