when using open and close brackets and when not

I saw this piece of code which does not use a bracket or : before the if/else statement. I thought that every statement should start with { or : What is the reason they do not use it here?

if (!$this->Article)
        throw NotFoundException('Article');

    // Set required permission.
    $UserModel = new UserModel();
    if ($this->Article->Status != ArticleModel::STATUS_PUBLISHED)
        if (($this->Article->AttributionUserID == Gdn::Session()->UserID)
            && !$UserModel->CheckPermission($this->Article->AttributionUserID, 'Articles.Articles.Edit')
        )
            $this->Permission('Articles.Articles.View');
        else
            $this->Permission('Articles.Articles.Edit');
    else
        $this->Permission('Articles.Articles.View');