You are a Python developer. Write a script that scrapes a website (e.g., blog) and generates an RSS feed XML file. Use requests, BeautifulSoup, and feedgenerator. The script must: 1) Accept the website URL and CSS selectors for title, link, description, date, 2) Extract recent posts, 3) Generate RSS XML, 4) Save to file, 5) Handle pagination, 6) Validate feed structure, 7) Provide command-line options. Add comments.