"> As far as I understand, the main reason of why Tab's original idea of using `$` has eventually been dropped was some uncertainty about its possible extensibility for being used in property _names_ besides property _values_.

The reason it got dropped is that some people (including Tab) do believe we should reserve $ for mixins and other preprocessor-like operations which may potentially be added to the language at some point. e.g. futuristic things like:

    @define apply-2d-transform(initial-scale, initial-rotation, ...) {
        ...
        my-transform-scaling: $initial-scale;
        my-transform-rotation: $initial-rotation;
        ...
        transform:
            scale(get(my-transform-scaling))
            rotate(get(my-transform-rotation))
            translate(get(my-transform-translation));
        will-change[]:
            transform;
    }

    .some-element {
        $apply-2d-transform(...);
        transition[]: transform 0.5s ease-in-out;
    }

    .some-element:hover {
        my-transform-scale: 1.1;
    }

I am convinced that at this point CSS is a clusterfuck that should be killed with fire.

Once an easy-to-use syntax is published, toolchains that parse CSS will update as fast as they can! But "--"? Everybody will stick to the old standard and never want to upgrade.

The rationale for the "--" sigil matches what I'd expected, but I don't understand: why not just `name: --value` ?

Running JavaScript in your browser automatically from any site that you visit is pretty darn scary when you think about it. You can protect from a whole host of vulnerabilities by disabling it, and then whitelisting only hosts which you trust.