The HTML 5 specification allows the omission of some optional start and end tags where the tags’ existence can be inferred.

View the source of this page. It validates despite its terseness. Browsers’ inspectors will show the missing tags.

Summary of the linked spec portion (not exactly correct but with the differences in minor semantics):

The following is then the smallest valid HTML document with a single paragraph:

<!DOCTYPE html><title>t</title><p>p

A small HTML document with a 3×3 table in it:

<!DOCTYPE html><title>xor</title>

index | 2019-03-23