Read more on MDN
let firstChild: WebAPI.DOMAPI.treeWalker => WebAPI.DOMAPI.node
let lastChild: WebAPI.DOMAPI.treeWalker => WebAPI.DOMAPI.node
let nextNode: WebAPI.DOMAPI.treeWalker => WebAPI.DOMAPI.node
let nextSibling: WebAPI.DOMAPI.treeWalker => WebAPI.DOMAPI.node
let parentNode: WebAPI.DOMAPI.treeWalker => WebAPI.DOMAPI.node
let previousNode: WebAPI.DOMAPI.treeWalker => WebAPI.DOMAPI.node
let previousSibling: WebAPI.DOMAPI.treeWalker => WebAPI.DOMAPI.node