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Once rules are deemed 'good enough', according to whatever the promotion criteria are, they can be promoted from the sandbox into core. TODO. We haven't quite solidified the promotion criteria for rules yet... see RulesProjPromotion for ongoing discussion.
Editing Another Developer's Sandbox
Editing another developer's sandbox rules is generally frowned upon.
However, if the rules have been promoted into core rules and no replies are received for 2 weeks from the original developer, updates can be made by other developers. It is still best practice to notify the original developer that that you're making the change. The revision control comments for the update should also clearly state that the rule was updated by another developer with the reason for the update.
(Note: this is documentation; if you want to read the historical planning docs, see RulesProjectPlan and RulesProjSandboxes.)
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