This relates to #12899. To support slices in this folder, we now get a file named cascade.toml with content:

[[cascade]]
  [cascade.params]
    color = 'red'
  [cascade.target]
    kind = 'page'
    lang = '{en,de}'
    path = '/books/**'
[[cascade]]
  [cascade.params]
    color = 'blue'
  [cascade.target]
    environment = 'production'
    kind = 'page'
    path = '/films/**'

We should consider allowing this also for the other map types:

• This would allow copy pasting examples from the docs without having to remove the root.
• Judging by the questions on the Hugo forum, it is a very common mistake to make.
• I don't see any obvious problem doing it this way, it should be reasonably simple to unwrap the root if needed.