planner: add docs for some variables (#9943)

[ti-chi-bot]

This is an automated cherry-pick of #9943

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[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• TomShawn

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[TomShawn]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

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Commit hash: d662fd3