Docs feedback: Unclear special keywords for gitlab-ci.yml "only" and "except"

https://docs.gitlab.com/ee/ci/yaml/README.html#onlyexcept-basic mention the special keywords:

Value	Description
api	When pipeline has been triggered by a second pipelines API (not triggers API).
triggers	For pipelines created using a trigger token.

It's not clear what "a second pipelines api" means - a link to the API doc would make this clearer. It's also not clear what the trigger jobs in https://docs.gitlab.com/ee/ci/multi_project_pipelines.html count as - again, a link to that documentation for the appropriate row would be clearer.