The Polymer.dart framework provides a set of Polymer (UI and other) components, but it will only work in the most recent versions of browsers: IE9, IE10, Safari 6, Firefox, and the latest Chrome (also for Android). It is important that in Polymer you can only have a single Dart script tag on an HTML document. Get started with creating a new Polymer application polymer1 by selecting the project template Web application (using the polymer library) in Dart Editor:

A new Polymer application

Inspecting pubspec.yaml will reveal the polymer dependency:

dependencies:
  polymer: any

Pub is invoked automatically, and installs polymer and a whole group of packages needed by polymer (such as mdv, observe, polymer_expressions, shadow_dom, and so on). We'll now examine in detail how a web component is defined in Polymer.