Man, even knowing that YAML document was going to be laden with bullshit, I only spotted the unquoted version strings looking fishy.

I also really dislike how often YAML is abused to take keys as list items. Something like this, for example:

hosts:
  debian-vm:
    user: root
  database-server:
    user: sql

"debian-vm" and "database-server" are the hostname, and as such they are values. So, this should be written as:

hosts:
  - name: debian-vm
    user: root
  - name: database-server
    user: sql

And I'm not just nitpicking here. If we change the example a bit:

hosts:
  database:
    user: sql

...then suddenly, you don't know, if "database" is just one of many possible hosts or if all hosts always have a shared database with this technology.