On google or DuckDuckGo syntax:

1. "Exact match" → for an exact string
2. SITE:url → search in a specified site
3. AFTER:1999 or BEFORE:2020 → before or after a specified date
4. 2020..2020 → search in a range
5. (A | B) → search results A or B
6. • → search for all results
7. FILETYPE:PDF → search for a specified filetype
8. RELATED:url → search related result of this URL
   9: CACHE:url → see the website that the search engine has in cache