Preview Release v2.0.0-rc.1

Meaningful Changes

The following notable changes have been made since the 2.0 Preview announcement.

• The config getter on element classes has been replaced by individual properties and
  observers getters, more closely resembling the 1.x syntax.

  static get properties() {
    return {
      aProp: String,
      bProp: Number
    }
  }
  static get observers() {
    return [
      '_observeStuff(aProp,bProp)'
    ]
  }

• 1.x-style dirty checking has been reinstated for better performance. An optional mixin is
  available for elements to skip dirty checking of objects and arrays, which may be more easy to
  integrate with some state management systems. For details, see
  Using the MutableData mixin in Data system concepts.

• Support for dynamically-created custom-style elements has been added.

• Support for the external style sheet syntax, <link rel="import" type="css"> has
  been added. This was deprecated in 1.x, but will be retained until an alternate solution is
  available for importing unprocessed CSS.

• New properties rootPath and basePath were added to Polymer.Element to allow authors
  to configure how URLs are rewritten inside templates. For details, see the
  Update URLs in templates in the Upgrade guide.