Neos\Neos\Domain\Service\UserInterfaceModeService::findModeByName PHP Method

    public function findModeByName($modeName)
    {
        if (isset($this->editPreviewModes[$modeName])) {
            if ($this->editPreviewModes[$modeName] instanceof UserInterfaceMode) {
                $mode = $this->editPreviewModes[$modeName];
            } elseif (is_array($this->editPreviewModes[$modeName])) {
                $mode = UserInterfaceMode::createByConfiguration($modeName, $this->editPreviewModes[$modeName]);
                $this->editPreviewModes[$modeName] = $mode;
            } else {
                throw new Exception('The requested interface render mode "' . $modeName . '" is not configured correctly. Please make sure it is fully configured.', 1427716331);
            }
        } else {
            throw new Exception('The requested interface render mode "' . $modeName . '" is not configured. Please make sure it exists as key in the Settings path "Neos.Neos.Interface.editPreviewModes".', 1427715962);
        }
        return $mode;
    }