9. HTML Comments

 

Comment is a piece of code which is ignored by any web browser. It is a good practice to add comments into your HTML code, especially in complex documents, to indicate sections of a document, and any other notes to anyone looking at the code. 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

Document content goes here..... This will produce following result without displaying the content given as a part of comments:

Document content goes here.....

Valid vs Invalid Comments

Comments do not nest which means a comment can not 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 given comment is a valid comment and will be wiped off by the browser.

Document content goes here..... 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.

< !-- This is not a valid comment --> Document content goes here..... This will produce following result:

< !-- This is not a valid comment --> Document content goes here.....

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 placed before the first line and end of the last line as shown in the given example below.

Example

Document content goes here..... This will produce following result:

Document content goes here.....

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.

Example

Document content goes here..... You will come across a situation where you will need to apply a different style sheet based on different versions of Internet Explorer, in such situation conditional comments will be helpful.

Using Comment Tag

There are few browsers that support tag to comment a part of HTML code.

Example

This is not Internet Explorer. If you are using IE then it will produce following result:

This is Internet Explorer.

But if you are not using IE, then it will produce following result:

This is not Internet Explorer.

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.

Example

--> Hello , World! This will produce following result:

Hello World!
Hello , World!

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 Casecading 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

-->

class="example">Hello , World!

This will produce following result:

Hello , World!

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