The Struts 2 documentation is maintained online and posted to the Apache Struts web site on a regular basis. A snapshot of the documentation is bundled with each distribution, so that people are able to refer to the documentation for that distribution.
The mechanism we use to integrate is wiki snapshot with the website distribution is covered by a JIRA ticket.
The HTML version of the documentation is maintained using the AutoExport plugin. (JAR annexed.)
The documentation "single sources" code segments using the Snippet macro. (JAR annexed.) For more about using snippets, see the Documentation Style Guide.