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This template is intended to be SUBSTITUTED (not transcluded) into Common_bugs pages at the time of their initial creation, while the release they document is still a pre-release. The use of <includeonly>safesubst:</includeonly> is to make nested substitution work correctly: the specified templates will not be expanded when the template page is saved or viewed, and will be transcluded instead of substituted if the template is (incorrectly) transcluded rather than substituted. This is as documented on Mediawiki's substitution page. The higher-level FedoraVersion and FedoraVersionNumber templates are not used here as they are not designed to work with substitution - they nest other templates using transclusion, so when substituted, the entire nested template is dumped into the page, which looks messy and does not result in the version being static, as intended. Usage: {{subst:Common_bugs_header_prerelease}} at the top of a common bugs page.