MDNSlot

mdn slot Slots are identified by their name attribute, and allow you to define placeholders in your template that can be filled with any markup fragment you want when the element is used. 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.

mdnslot login, The slot> tag is a placeholder inside a web component that you can fill with your own markup, which lets you create separate DOM trees and present them together. Use the template>.