code: function checkComponents (options) {
    for (const key in options.components) {
      const lower = key.toLowerCase()
      if (isBuiltInTag(lower) || config.isReservedTag(lower)) {
        warn(
          'Do not use built-in or reserved HTML elements as component ' +
                  'id: ' + key
        )
      }
    }
  }
docs: Validate component names