Extend job rules with multiple !reference containing array of rules

GitLab CI/CD
2

Thanks for this post - I had this exact same question. The docs for rules say

You can use !reference tags to reuse rules configuration in different jobs.

But and when I click through to reuse rules configuration, I see this example:

.default_rules:
  rules:
    - if: $CI_PIPELINE_SOURCE == "schedule"
      when: never
    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH

job1:
  rules:
    - !reference [.default_rules, rules]
  script:
    - echo "This job runs for the default branch, but not schedules."

job2:
  rules:
    - !reference [.default_rules, rules]
    - if: $CI_PIPELINE_SOURCE == "merge_request_event"
  script:
    - echo "This job runs for the default branch, but not schedules."
    - echo "It also runs for merge requests."

Putting this in the pipeline editor results in:

".default_rules":
  rules:
  - if: $CI_PIPELINE_SOURCE == "schedule"
    when: never
  - if: "$CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH"
job1:
  rules:
  - - if: $CI_PIPELINE_SOURCE == "schedule"
      when: never
    - if: "$CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH"
  script:
  - echo "This job runs for the default branch, but not schedules."
job2:
  rules:
  - - if: $CI_PIPELINE_SOURCE == "schedule"
      when: never
    - if: "$CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH"
  - if: $CI_PIPELINE_SOURCE == "merge_request_event"
  script:
  - echo "This job runs for the default branch, but not schedules."
  - echo "It also runs for merge requests."

I don’t find any place saying how rules supports nested arrays, so the expected behavior here is ambiguous. I’d like to request that the docs be updated. What is the expected behavior?