An HTML comment is used to add explanatory notes to the markup or to prevent the browser from interpreting specific parts of the document.
Comments start with the string <!-- and end with the string -->, generally with text in between. This text cannot start with the string > or ->, cannot contain the strings --> or --!>, nor end with the string <!-, though <! is allowed.
The browser ignores comments as it renders the code. In other words, they are not visible on the page - just in the code. HTML comments are a way for you to write helpful notes about your code or logic.
The above is true for XML comments as well. In addition, in XML, such as in SVG or MathML markup, a comment cannot contain the character sequence --.
Comments can be used on a single line, or span multiple lines. They can be used in the following places:
- Before and after the Doctype
- Before and after the
<html>element - As the content of most elements except:
<script>,<style>,<title>,<textarea>, because these elements interpret their content as raw text
Note: While <script> elements should not have HTML comments and should use JavaScript comments instead, there was a legacy practice to enclose the whole script content in an HTML comment so ancient browsers that don't support JavaScript don't render it as text. This is now a legacy feature of JavaScript itself and you should not rely on it.