Comments are ignored by XML parsers. Comments are used to describe XML or leave a note for humans reading the XML. Both HTML and XML support comments and they both use the same syntax:

<!-- my comments -->

where the anything enclosed inside <!-- and --> is a comment. Example:

<?xml version="1.0"?>
<!-- canadian taxes -->
<taxes>
  <federal_income>15% - 35%</federal_income>
  <alberta_income>10%</alberta_income>
  <GST>5%</GST>
</taxes>

XML comments can also be used to comment out XML tags.