What does the \'i\' modifier do in CSS attribute selectors?

Unveiling the Enigma of "i" in CSS Attribute Selectors

In the realm of CSS, the enigmatic letter "i" has emerged within attribute selectors, leaving many perplexed. To unravel its mystery, let's delve into its purpose and discover the significance it brings to web styling.

What is 'i' in a CSS Attribute Selector?

The "i" modifier in a CSS attribute selector signifies case-insensitive attribute matching. This feature, introduced in CSS Selectors Level 4, allows for flexibility in matching HTML attributes irrespective of their capitalization.

How Does It Work?

Consider the following code snippet:

[type="checkbox" i]

This selector would match all checkbox input elements, regardless of whether their 'type' attribute is in uppercase, lowercase, or a mix of both. In other words, it would match elements with the attributes 'type="Checkbox"', 'type="cHeCkBoX"', and so on.

Historical Context and Availability

Case-insensitive attribute matching was initially introduced in Chrome's user-agent styles but could later be enabled for web content through experimental features flags. It has since gained widespread support in modern browsers, including Chrome 49 , Firefox 47 , Safari 9 , and Opera 37 *.

Example and Browser Test

To demonstrate the functionality, let's consider a selector that sets a green background color for elements with the attribute 'data-test="a"' or 'data-test="A"'.

[data-test] {
    width: 100px;
    height: 100px;
    margin: 4px;
}

[data-test="A"] {
    background: red;
}

[data-test="a" i] {
    background: green;
}

If this code is applied to the following HTML:

<div data-test="A"></div>

The resulting element will have a green background if case-insensitive attribute matching is supported in the browser and red if not.

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