From Last Outlaws Online

Documentation This is a documentation subpage for Template:Check date (see that page for the template itself).
It contains usage information, categories and other content that is not part of the original template page.

This meta-template accepts one parameter. If the parameter is empty, it produces the text "Date?" and adds it to Category:Pages with Dateless Templates; otherwise, it echoes the parameter back.

It is used in templates with dates to display the date that the template was added.