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+# ReactiveElement 1.0
+
+[![Build Status](https://github.com/lit/lit/workflows/Tests/badge.svg)](https://github.com/lit/lit/actions?query=workflow%3ATests)
+[![Published on npm](https://img.shields.io/npm/v/@lit/reactive-element?logo=npm)](https://www.npmjs.com/package/@lit/reactive-element)
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+
+# ReactiveElement
+
+A simple low level base class for creating fast, lightweight web components.
+
+## About this release
+
+This is a stable release of `@lit/reactive-element` 1.0.0 (part of the Lit 2.0 release). If upgrading from previous versions of `UpdatingElement`, please see the [Upgrade Guide](https://lit.dev/docs/releases/upgrade/).
+
+## Documentation
+
+Full documentation is available at [lit.dev](https://lit.dev/docs/api/ReactiveElement/).
+
+## Overview
+
+`ReactiveElement` is a base class for writing web components that react to changes in properties and attributes. `ReactiveElement` adds reactive properties and a batching, asynchronous update lifecycle to the standard web component APIs. Subclasses can respond to changes and update the DOM to reflect the element state.
+
+`ReactiveElement` doesn't include a DOM template system, but can easily be extended to add one by overriding the `update()` method to call the template library. `LitElement` is such an extension that adds `lit-html` templating.
+
+## Example
+
+```ts
+import {
+  ReactiveElement,
+  html,
+  css,
+  customElement,
+  property,
+  PropertyValues,
+} from '@lit/reactive-element';
+
+// This decorator defines the element.
+@customElement('my-element')
+export class MyElement extends ReactiveElement {
+  // This decorator creates a property accessor that triggers rendering and
+  // an observed attribute.
+  @property()
+  mood = 'great';
+
+  static styles = css`
+    span {
+      color: green;
+    }
+  `;
+
+  contentEl?: HTMLSpanElement;
+
+  // One time setup of shadowRoot content.
+  createRenderRoot() {
+    const shadowRoot = super.createRenderRoot();
+    shadowRoot.innerHTML = `Web Components are <span></span>!`;
+    this.contentEl = shadowRoot.firstElementChild;
+    return shadowRoot;
+  }
+
+  // Use a DOM rendering library of your choice or manually update the DOM.
+  update(changedProperties: PropertyValues) {
+    super.update(changedProperties);
+    this.contentEl.textContent = this.mood;
+  }
+}
+```
+
+```html
+<my-element mood="awesome"></my-element>
+```
+
+Note, this example uses decorators to create properties. Decorators are a proposed
+standard currently available in [TypeScript](https://www.typescriptlang.org/) or [Babel](https://babeljs.io/docs/en/babel-plugin-proposal-decorators). ReactiveElement also supports a [vanilla JavaScript method](https://lit.dev/docs/components/properties/#declaring-properties-in-a-static-properties-field) of declaring reactive properties.
+
+## Installation
+
+```bash
+$ npm install @lit/reactive-element
+```
+
+Or use from `lit`:
+
+```bash
+$ npm install lit
+```
+
+## Contributing
+
+Please see [CONTRIBUTING.md](../../CONTRIBUTING.md).