DefinitelyTyped/types/prefixfree/prefixfree-tests.ts

window.StyleFix === StyleFix;
window.PrefixFree === PrefixFree;

StyleFix.register((css, raw, element) => {
    return css + "\n/* Custom end comment */\n";
});
StyleFix.process();

const browser = (() => {
    switch (PrefixFree.prefix) {
        case "-moz-":
            return "firefox";
        case "-ms-":
            return "ie";
        case "-o-":
            return "opera";
        case "-webkit-":
            return "chrome";
        default:
            return "unknown";
    }
})();

// $ExpectError
if (browser === "safari") {
    // There's no way to differentiate Safari from Chrome using just prefixes
}