NSRuleEditor only allow criterion row to be added once

I have an object that is an NSRuleEditorDelegate for an NSRuleEditor whose nestingMode is NSRuleEditorNestingModeList. There are 8 different possible criteria. Each criterion is optional but at least 1 is required (ruleEditor.canRemoveAllRows = NO). Each criterion should only be added once. How can I limit adding a criterion for a row if it is already in the editor at a different row?

Thanks!

NSRuleEditor only allow criterion row to be added once
 
 
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