"Prior agreement" means prior to committing to head, or the release. A simple vote in bugzilla or on developer mailing lists is good if it is controversial, or if it is considered obvious by component lead, then a formal voting record is not needed, but, would be subject to retroactive veto if later found objectionable by a committer to a component. In the event of disagreement between committers that can not be resolved, then the PMC can arbitrate a solution The PMC would normally strive to satisfy all committer requests, but may vary priority, schedule or which release a change occurs in, or the PMC might suggest other technical solutions be investigated.