chromium/third_party/blink/web_tests/external/wpt/css/css-properties-values-api/support/alt/alt.js

function reg_url(name, inherits) {
    CSS.registerProperty({
        name: name,
        syntax: '<url> | none',
        inherits: inherits,
        initialValue: 'none'
    });
}

reg_url('--reg-alt-non-inherited-url', false);
reg_url('--reg-alt-non-inherited-func', false);