MDNSlot

mdn slot element .slot = aString. A DOMString. The definition of 'slot' in that specification. The slot property of the Element interface returns the name of the shadow DOM slot attached to the element. A. 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>

mdnsport, 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.