docs: function getElementRegistry(identifier) {
    if (!window.__private__) window.__private__ = {};
    if (window.__private__.elementRegistry === undefined) window.__private__.elementRegistry = {};
    if (typeof identifier === 'string') {
      if (!~identifier.indexOf('-')) identifier = identifier + '-element';
      return window.__private__.elementRegistry[identifier];
    }
    if (typeof identifier === 'function') {
      for (let tag in window.__private__.elementRegistry) {
        let Class = window.__private__.elementRegistry[tag];
        if (Class.__proto__ === identifier) return Class;
      }
      return null;
    }
    return window.__private__.elementRegistry;
  }