Auto Blocking

This heading and image are plain content, not an authored block. buildAutoBlocks turns them into a hero block automatically because the image directly precedes the page's first heading.

Auto-detected embed

A bare YouTube link, with no block authored around it:

https://www.youtube.com/watch?v=4PZuPLvh-7k

buildEmbedBlocks wraps it into an embed block in place. Scroll it into view to trigger the lazy-loaded iframe.

Not auto-blocked

This section has an image but no adjacent heading pattern, and no video link, so it stays as plain content.