This element is compatible with Polymer 0.5 and lower only, and will be deprecated.
You can check out a similar 0.8-compatible version of this element at https://github.com/polymerelements/iron-doc-viewer
Note If you update elements in this repo, you'll need to rebuild build.sh in core-component-page-dev so they're used in the compiled version (core-component-page).