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For examples of extensions using this hook, see Category:CampaignEventsGetPolicyMessageForRegistrationForm extensions . Category:Extension hooks#CampaignEventsGetPolicyMessageForRegistrationForm Category:Undocumented extension hooks#CampaignEventsGetPolicyMessageForRegistrationForm Category:Extension hooks provided by CampaignEvents Category:Extension hooks#CampaignEventsGetPolicyMessageForRegistrationForm Category:Undocumented extension hooks#CampaignEventsGetPolicyMessageForRegistrationForm Category:Extension hooks provided by CampaignEvents