Checkbox to add to cart on listing page for "related" items

[NMTEACO]

I just finished a template recently which includes the necessary coding. Just haven't had time to list it yet

I assume I just need to replace the buy now button

<input type="button" value="[category_buyitlink]" onclick="window.location = 'add_cart.asp?quick=1&amp;item_id=[catalogid]'" class="btn" onmouseover="this.className='btn_over'" onmouseout="this.className='btn'" />

in the code bellow with a checkbox. I just cant figure out how to get the "add to cart" button to see which items are checked and add them to the cart. I did it before, but it was so long ago I forgot what to do!

<!--START: accessories_0-->
    <div class="accessoriesBlock">
      <div class="header">
        <h3>[product_Header-accessories]</h3>
        <div class="clear"></div>
      </div>
      <!--START: accessories_items0-->
          <div class="product-item alternative">
            <div class="img"><a href="product.asp?itemid=[catalogid]"><img src="[THUMBNAIL]" alt="[name]" /></a></div>
            <div class="name"><a href="product.asp?itemid=[catalogid]">[name]</a></div>
            <div class="stars">
            <!--START: product_review--> 
            <!--START: product_review_average-->
                <img src="assets/templates/common-html5/images/star[review_average].png" alt="Average Rating" /><span>([review_count])</span>
                <div class="clear"></div>
            <!--END: product_review_average--> 
            <!--END: product_review-->
            </div>
            <div class="price"><!--START: ITEMPRICE--> 
            <span class="hidden">[product_yourprice]&nbsp;</span>[ITEMPRICE]
            <!--END: ITEMPRICE--> 
            <!--START: SALEPRICE-->
            <div class="on-sale">[product_sale]</div>
            <del class="price2">[ITEMPRICE]&nbsp;</del>
            <span class="hidden">[product_onsale]&nbsp;</span>[ITEMSALEPRICE]
            <!--END: SALEPRICE--></div>
            <div class="status"><!--START: product_availability-->[availability] <!--END: product_availability--><!--START: freeshippingblock-->[freeshipping]<!--END: freeshippingblock--></div>
            <div class="action">
                <input type="button" value="[category_buyitlink]" onclick="window.location = 'add_cart.asp?quick=1&amp;item_id=[catalogid]'" class="btn" onmouseover="this.className='btn_over'" onmouseout="this.className='btn'" />
            </div>
        <div class="clear"></div>
        </div>
      <!--END: accessories_items0--> 
    </div>
    <div class="clear"></div>
    <!--END: accessories_0--> 

[thecartdesigner]

I have an html5 listing template with all of the options you need. 3dcart never adding the coding for different types (qty box and checkbox) of "Related" and "Accessories" which is "Upsell" in the product page related tab. So they have the selectable function type in the category advance options... But no code to go with it.

I just finished a template recently which includes the necessary coding. Just haven't had time to list it yet

[NMTEACO]

A few years ago I remember that there was a template that had it so that you could add related items to the card when you checked out by selecting them on the listing page. All I can find on the support site is about "upsell" which allows you to add the items after checkout out, but this was a way to add them before you added the main item to the cart.

Does anyone have any idea what im talking about, and remember the code to use?