Well, actually 8cd9cde won't work, unless we put the
`|to_nice_yaml` thing on a new line.
We can, but that takes more lines and makes things look uglier.
Using `|to_json` seems good enough.
The whole file is parsed as YAML later on and merged with the
`_extension` variable before being dumped as YAML again in the end.
c13c29f48e