Comment is a piece of code which is
ignored by any web browser Comments help you and others understand your code
and increases code readability.
HTML comments are placed in
between <!-- ... --> tags. So, any content placed with-in
<!-- ... --> tags will be treated as comment and will be completely
ignored by the browser.
Example
<html>
<head>
<!-- Document Header Starts -->
<title>This is document title</title>
</head> <!-- Document Header Ends
-->
<body>
<p>Document content goes here.....</p>
</body>
</html>
Comments do not nest which means a
comment cannot be put inside another comment. Second the double-dash sequence
"--" may not appear inside a comment except as part of the closing
--> tag. You must also make sure that there are no spaces in the start-of
comment string.
Example
Here, the given comment is a valid
comment and will be wiped off by the browser.
<html>
<head>
<title>Valid Comment Example</title>
</head>
<body>
<!--
This is valid comment -->
<p>Document content goes here.....</p>
</body>
</html>
But, following line is not a valid
comment and will be displayed by the browser. This is because there is a space
between the left angle bracket and the exclamation mark.
<head>
<title>Invalid Comment Example</title>
</head>
<body>
< !--
This is not a valid comment -->
<p>Document content goes here.....</p>
</body>
</html>
Multiline Comments
So far we have seen single line
comments, but HTML supports multi-line comments as well.
You can comment multiple lines by the
special beginning tag <!-- and ending tag --> placed before the first
line and end of the last line as shown in the given example below.
Example
<html>
<head>
<title>Multiline Comments</title>
</head>
<body>
<!--
This is a multiline comment and it can
span through as many as lines you
like.
-->
<p>Document content goes here.....</p>
</body>
</html>
Conditional Comments
Conditional comments only work in
Internet Explorer (IE) on Windows but they are ignored by other browsers. They
are supported from Explorer 5 onwards, and you can use them to give conditional
instructions to different versions of IE.
<html>
<head>
<title>Conditional Comments</title>
<!--[if IE 6]>
Special instructions for IE 6 here
<![endif]-->
</head>
<body>
<p>Document content goes here.....</p>
</body>
</html>
Using Comment Tag
There are few browsers that support
<comment> tag to comment a part of HTML code.
Note − The <comment> tag
deprecated in HTML5. Do not use this element.
<html>
<head>
<title>Using Comment Tag</title>
</head>
<body>
<p>This is <comment>not</comment>
Internet Explorer.</p>
</body>
</html>
Commenting Script Code
Though you will learn JavaScript with
HTML, in a separate tutorial, but here you must make a note that if you are
using Java Script or VB Script in your HTML code then it is recommended to put
that script code inside proper HTML comments so that old browsers can work
properly.
<html>
<head>
<title>Commenting Script Code</title>
<script>
<!--
document.write("Hello
World!")
//-->
</script>
</head>
<body>
<p>Hello , World!</p>
</body>
</html>
Commenting Style Sheets
Though you will learn using style sheets
with HTML in a separate tutorial, but here you must make a note that if you are
using Cascading Style Sheet (CSS) in your HTML code then it is recommended to
put that style sheet code inside proper HTML comments so that old browsers can
work properly.
Example
<html>
<head>
<title>Commenting Style Sheets</title>
<style>
<!--
.example {
border:1px solid #4a7d49;
}
//-->
</style>
</head>
<body>
<div class = "example">Hello
, World!</div>
</body>
</html>
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