[laimas]

Ну как это понимать в контексте кнопки "Выбрать все"?

<div class="upsale__block__sub-right-wrap">
    <div class="upsale__block__bot-right__title-wrap dflex">
        <div class="upsale__block__bot-right__title dflex">
            <input id="floor" type="checkbox" class="block__check" disabled />                            
        </div>                           
    </div>
    <div class="upsale__block__bot-right__sub-wrap dnone">
        <div class="montage__content-wrap">
            <span class="montage__text">intro text where we explain </span>
            <div class="montage__floor-wrap montage__comp-wrap dflex">
                <div class="montage__floor dflex">
                    <div class="floor__item-wrap">
                        <div class="floor__item-inner">
                            <div class="floor__item">
                                <input type="checkbox" name="groundfloor" value="groundfloor">
                                <div class="floor__item__img">
                                    <img src="catalog/view/theme/myown/image/floor/groundFloor.svg" alt="">
                                </div>
                                <span class="floor__item__text">floor__item__text 0</span>
                            </div>
                            <div class="floor__item">
                                <input type="checkbox" name="groundfloor" value="groundfloor">
                                <div class="floor__item__img">
                                    <img src="catalog/view/theme/myown/image/floor/groundFloor.svg" alt="">
                                </div>
                                <span class="floor__item__text">floor__item__text 1</span>
                            </div>
                        </div>
                    </div>                                       
                </div>
            </div>
        </div>           
    </div>           
</div>

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
<script>
$('div.upsale__block__sub-right-wrap').on('change', 'input', function(e) {
    var chk = $(e.delegateTarget).find('input');
    if(chk.eq(0)[0]==this) chk.slice(1).prop('checked', this.checked);
    else {
        var c = chk.slice(1).filter(':checked').length;
        chk.eq(0).prop({checked: c, disabled: !c});    
    }
})
</script>

Где логика в работе этого флажка?