All components FOUC the page regardless of resource load timing or page caching

[csuwildcat]

Not sure if this is already something you're looking at with these new non-X-tag components, but I noticed all the new versions of these components flash a broken state regardless of when they are loaded, or if the page is cached.

[potch]

Yep- it's an unfortunate side effect of HTMLImports not blocking page load. Polymer offers an [unresolved] attribute for the purposes of obscuring the FOUC, which we will likely use and document as a best practice. Most complex webapps have a splash screen, and perhaps even a <splash-screen> is something developers may want.