The purpose of starting an initial comment with /*! in JavaScript and CSS files

Question

I've noticed that initial comment in JavaScript or CSS files is sometimes started with /*!. What is the purpose of the explanation mark?

For example, jQuery:

/*! jQuery v1.7.1 jquery.com | jquery.org/license */

Bootstrap:

/*!
 * Bootstrap v2.0.1
 *
 * Copyright 2012 Twitter, Inc

Answer 1

It tells compression tools such as the YUICompressor and Uglify, which minify the code, to leave the commented section in place as they usually remove all comments from the code.

• Kevin: Is there a way to override this without removing the !? I'm using Uglify and I need to remove all blocks so I can inject the CSS file into my HTML.
• Asfand Qazi: Of course, the point of leaving these comments in, usually, is because they are licensing messages that are required to be included with any distributed versions of the code.
• keaukraine: Licenses are meant to be always present with code so you may violate some rights by removing them.
• Peter Mortensen: Now deprecated?

Answer 2

Some software like Coda also support the "bookmark syntax" shown below, so that one can navigate to different parts of code through the app's code navigator.

// !bookmark
/* !bookmark */
<!-- !bookmark -->

Note that in the examples above there's a space between the comment syntax the exclamation mark.

Answer 3

I believe one purpose of the exclamation point is to tell JavaScript minifiers to leave these particular comments in, when condensing the files.

Answer 4

It is also important for attribution for the author of external dependencies/API, especially free ones.

When minifying, the least we can do is to offer them some bytes of recognition.

e.g. /*! PhotoSwipe main CSS by Dmitry Semenov | photoswipe.com | MIT license */ will not be erased by minifier.