Auto teaser runs only when Auto teaser is Yes, the context is a full article, there is no {elock} block, and the visitor is not allowed.
- Paragraphs: keep the first N block-level chunks (default 2).
- Read more: show introtext and hide fulltext. Falls back to paragraphs if there is no Read more break.
If a shortcode exists on the article, auto teaser does not run. Shortcode wins.