HTML Comments:
<!-- <div> This div will not show </div> -->
CSS Comments:
/* This style will not apply */
JavaScript Comments:
// This single line JavaScript code will not execute
OR
/*
The whole block of JavaScript code will not execute
*/
Reason of comments:
HTML Comments
<!-- Everything is invisible -->
To comment block with nested comments: substitute inner (block) comments from "--" to "++"
<!-- *********************************************************************
* IMPORTANT: To uncomment section
* sub inner comments "++" -> "--" & remove this comment
*********************************************************************
<head>
<title>My document's title</title> <++! My document's title ++>
<link rel=stylesheet href="mydoc.css" type="text/css">
</head>
<body>
<++! My document's important HTML stuff ++>
...
...
...
</body>
*********************************************************************
* IMPORTANT: To uncomment section
* sub inner comments "++" -> "--" & remove this comment
*********************************************************************
-->
Thus, the outer most comment ignores all "invalid" inner (block) comments.
Just create a multi-line comment around it. When you want it back, just erase the comment tags.
For example, <!-- Stuff to comment out or make inactive -->
Use:
<!-- This is a comment for an HTML page and it will not display in the browser -->
For more information, I think 3 On SGML and HTML may help you.
If you are using Eclipse then the keyboard shortcut is Ctrl + Shift + / to add a group of code. To make a comment line or select the code, right click -> Source -> Add Block Comment.
To remove the block comment, Ctrl + Shift + \ or right click -> Source -> Remove Block comment.
Source: Stackoverflow.com