How to use the @observablehq/stdlib.Library function in @observablehq/stdlib

export default function load(notebook, library, observer) {
  if (typeof library == "function") observer = library, library = null;
  if (typeof observer !== "function") throw new Error("invalid observer");
  if (library == null) library = new Library();

  const {modules, id} = notebook;
  const map = new Map;
  const runtime = new Runtime(library);
  const main = runtime_module(id);

  function runtime_module(id) {
    let module = map.get(id);
    if (!module) map.set(id, module = runtime.module());
    return module;
  }

  for (const m of modules) {
    const module = runtime_module(m.id);
    let i = 0;
    for (const v of m.variables) {

export default function Runtime(builtins = new Library, global = window_global) {
  var builtin = this.module();
  Object.defineProperties(this, {
    _dirty: {value: new Set},
    _updates: {value: new Set},
    _computing: {value: null, writable: true},
    _init: {value: null, writable: true},
    _modules: {value: new Map},
    _variables: {value: new Set},
    _disposed: {value: false, writable: true},
    _builtin: {value: builtin},
    _global: {value: global}
  });
  if (builtins) for (var name in builtins) {
    (new Variable(TYPE_IMPLICIT, builtin)).define(name, [], builtins[name]);
  }
}