Dartdoc is typically used as a command line utility to support generating documentation served on websites. In the future this directory may contain direct examples, but for now, here are pointers to the main users of dartdoc in the Dart ecosystem.
Note, unlike the other two examples, here dartdoc is used as a library. While we make some effort not to regularly break simple uses of the library interface, we strongly recommend you use the command line and focus our semantic versioning around that case. However, if that doesn't work for your case, the pub site usage may be of interest. See this script for the entry point.