chromium/third_party/blink/renderer/core/speculation_rules/README.md

Flexible syntax for defining what outgoing links are eligible to be prepared speculatively before navigation. Enables access to additional enhancements, such as use of a private prefetch proxy, where applicable.

https://github.com/jeremyroman/alternate-loading-modes/blob/main/triggers.md
https://wicg.github.io/nav-speculation/speculation-rules.html