From Fedora Project Wiki

This template is intended to be SUBSTITUTED (not transcluded) into Common_bugs pages at the time a release goes stable, replacing the pre-release header which is generated by substitution of Template:Common_bugs_header_prerelease. The use of <includeonly>safesubst:</includeonly> is to make nested substitution work correctly: the specified template 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_stable_release<|release=NN>}} at the top of a common bugs page. If release is not specified, current stable version is assumed - ENSURE THAT Template:CurrentFedoraVersion IS SET TO THE NEW RELEASE VERSION!