Prefixed CSS first (css-prefix-order)

Ensure vendor-prefixed versions of a CSS property are listed before the standardized, unprefixed version.

Why is this important?

When multiple versions of the same CSS property are specified, the last supported one will be used due to how browsers handle fallback values. This means the order matters when using both vendor-prefixed and unprefixed versions of the same property. Specifically, the unprefixed version must be listed last to ensure standardized behavior takes precedence.

What does the hint check?

This hint examines CSS files looking for blocks containing both prefixed and unprefixed CSS properties or values. The hint then verifies the last listed version of a particular property in a block is unprefixed.

Examples that trigger the hint

appearance: none;
-moz-appearance: none;
-webkit-appearance: none;

display: grid;
display: -ms-grid;

Examples that pass the hint

-moz-appearance: none;
-webkit-appearance: none;
appearance: none;

display: -ms-grid;
display: grid;

How to use this hint?

This package is installed automatically by webhint:

npm install hint --save-dev

To use it, activate it via the .hintrc configuration file:

{
    "connector": {...},
    "formatters": [...],
    "parsers": [...],
    "hints": {
        "css-prefix-order": "error"
    },
    ...
}

Note: The recommended way of running webhint is as a devDependency of your project.