Yes, the state of the Ansible documentation is a mess unfortunately.
Code is commited in without documentation, sometimes the documentation is added in a later commit but this commit is not merged in to all the correct branches.
I tried once to get a commit merged inn, but nothing happened so I guess documentation is low priority and the time is used on creating new stuff, hopefully with documentation :-)
So the best thing is to use the latest documentation called devel since that more updated and relevant.
An there you see intro_configuration is quite different
https://docs.ansible.com/ansible/devel/intro_configuration.html
--
Kai Stian Olstad