The CDK customizes quite a few things in the build process. One aspect of that is custom JavaDoc tags, such as @cdk.githash (source of the Taglet). This tag replaced a similar tag for Subversion (@cdk.svnrev) and allowed a link to the matching source code for that class, for which we have not found another way to achieve that. This linking functionality was broken for a while, but is now fixed again:
The last line also shows the branch name now, instead of always master, thanx to GitHub's link-to-friendly URIs for Git repository content.
Additionally, not all classes have this tag yet, and I have created a Junior Job for that.