What Does the `\9` in CSS Width Declarations Do?

Understanding the Meaning of 9 in CSS Width Declarations

CSS code can include a special character, 9, that serves as a "CSS hack" specifically targeting Internet Explorer versions 7, 8, and 9. When used at the end of a CSS property declaration, as in the example below:

width: 500px;

this trick ensures that the property is only applied within those particular versions of Internet Explorer. Other browsers will ignore this hack altogether.

In the provided example, the width property will set the element's width to 500 pixels, but only when viewed in IE 7, 8, or 9. All other browsers will disregard the 9 suffix and will not apply the width rule.

This hack allows developers to create CSS rules that are specific to certain browsers or browser versions. For instance:

#myElement {
    width: 300px;
    width: 500px;
}

With this code, the element will be 500 pixels wide in IE 7, 8, and 9, while in all other browsers, it will be 300 pixels wide.

Please note that this hack also works in Internet Explorer 10, as specified in an edit to the original answer.

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