What Does the \'i\' Modifier Mean in CSS Attribute Selectors?

Understanding the CSS Attribute Selector "i"

When exploring the CSS stylesheet of the Google Chrome user agent, you may encounter a selector like the following:

[type="checkbox" i]

This enigmatic "i" symbol prompts the question: what significance does it hold?

Answer:

The "i" is an abbreviated attribute that indicates whether the selector should use case-insensitive attribute matching. This feature, introduced in CSS Selectors Level 4, has been implemented in major browsers such as Chrome, Firefox, and Safari.

The "i" modifier ensures that when searching for an element with a specific attribute value, the browser will consider both uppercase and lowercase values. This is particularly useful in cases where the casing of attribute values is inconsistent or not standardized.

Working Example:

Consider the following CSS snippet:

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

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

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

When applied to an HTML document containing the following element:

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

If the browser supports case-insensitive attribute matching, the div will be colored green, indicating that the "a" attribute value (in lowercase) is considered equivalent to the "A" attribute value used in the selector. Otherwise, the div will be colored red.

This feature enhances the flexibility and robustness of CSS selectors, reducing the potential for breaking changes due to inconsistent attribute casing.

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