Template, slot, and shadow

mdn slot An element with a slot attribute is assned to the slot created by the slot> element whose name attribute's value matches that slot attribute's value.. The slot property of the Element interface returns the name of the shadow DOM slot the element is inserted

mdn slot link alternatif, The slot> HTML element—part of the Web Components technology suite—is a placeholder inside a web component that you can fill with your own markup, which lets you create separate.