iframes and Shadow DOM, Piercing Nested Contexts

What's the key DIFFERENCE between iframes and shadow DOM for a scraper?

• AThere is no difference
• Biframes are full embedded documents (must 'switch into' via frame_locator); shadow DOM is a scoping mechanism on a host element (Playwright pierces open shadow DOM automatically)
• CShadow DOM is always cross-origin
• Diframes don't exist in modern browsers