https://www.polymer-project.org/platform/custom-elements.html has a 404 for the "Shadow dom" button

[Pomax]

It looks like it's still pointing to the old style URLs (https://www.polymer-project.org/docs/start/shadow-dom.html instead of https://www.polymer-project.org/platform/shadow-dom.html), which might in fact be the case for tons of buttons on other pages and probably warrants a quick grep

[ebidel]

This issue was moved to Polymer/old-docs-site#779