```js
// YourPage.js

import { LitElement, html } from 'lit-element';

class DocumentScreen extends LitElement {
  static get properties() {
    return {
      _data: { type: Object },
      _status: { state: true },
    };
  }

  constructor() {
    super();
    this._status = 'idle';
  }

  connectedCallback() {
    super.connectedCallback();
    this.fetchData();
  }

  fetchData() {
    this._status = 'loading';

    fetch('https://your-restful-endpoint')
      .then((response) => {
        if (!response.ok) {
          throw new Error('Network response was not ok');
        }
        response.json();
      })
      .then((data) => {
        this._status = 'success';
        this._data = data;
      })
      .catch((error) => {
        this._status = 'error';
      });
  }

  render() {
    if (this._status === 'error') {
      return html`<p>There was an error fetching the data!</p>`;
    }

    if (this._status === 'loading') {
      return html`<p>Loading...</p>`;
    }

    const { user, document, subdocuments } = this._data;
    return html`
      <demo-page-layout .user=${user}>
        <demo-document-header .document=${document}></demo-document-header>
        <demo-document-list .documents=${subdocuments}></demo-document-list>
      </demo-page-layout>
    `;
  }
}

customElements.define('demo-document-screen', DocumentScreen);
```