Where is the example theme?

The plone.app.theming manual says that Plone ships with an example theme. However, this example theme does not seem to be part of my Plone 5.0.6 installation, since the only theme I can see in the theme overview is the Barceloneta theme. So where can I find this example theme?

There used to be a Twitter bootstrap example theme, but you can find other Plone 5 themes on the https://plone.org/download page

(filed an issue https://github.com/plone/plone.app.theming/issues/120)