Element: slot property - Web APIs | MDN - MDN Web Docs

mdn slotelement .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. AWhen the slot's containing component gets rendered, the slot is rendered with the custom element's child that has a matching slot attribute. A named slot is a slot> element