In CSSProperties.json, properties can be defined with "auto-functions":true, this generates a style builder like

    static void applyValueOrphans(BuilderState& builderState, CSSValue& value)
    {
        if (downcast<CSSPrimitiveValue>(value).valueID() == CSSValueAuto) {
            builderState.style().setHasAutoOrphans();
            return;
        }
        builderState.style().setOrphans(downcast<CSSPrimitiveValue>(value));
    }

However, this is useless if the parser doesn't accept `auto` as a valid keyword!

So I think that an error should be reported if parser-grammar doesn't contain "auto", or something like that.
Or maybe don't require that but let auto-functions automatically imply that `auto` is a valid keyword.

But the current state is bad, it means that orphans:initial doesn't map to any value of its grammar, and getComputedStyle().orphans can return "auto" which is not a supported value.

Both `orphans` and `widows` are affected.