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By default related products are displayed under buybox form as a list with Related product tile and add to cart checkboxes.
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Using this form user can add selected products to cart (possibly all of them) along with the main product with one click.
A bunch of settings can be added and adjusted via xml (catalog_product_view.xml)e.g headline, subheadline, items limit, add to cart button/checkbox.
Possible adjustments (they require additional work - not given by default in this module): display this section as products carousel.