I wouldn't call KDL "established"; it's honestly pretty niche. It looks _similar_ to pre-existing configuration formats, but KDL is very picky about syntax. I.e.: single word string MUST be quoted.

In this same space, https://codeberg.org/emersion/scfg/ is pretty widely used. The curious thing about scfg is that it's not really a "new" format: the syntax described has been in use by different tools for decades. They just didn't call it scfg, and it's mostly the name itself that's new.

It is picky, but picky is good. It's explicit which creates uniformity.

For example with niri, if you forget quotes on a string value, you get this error.

    $ niri validate
    Error:   × error loading config
      ├─▶ error parsing
      ╰─▶ error parsing KDL

    Error:   × identifiers cannot be used as arguments
        ╭─[config.kdl:42:1]
     42 │         // Disable acceleration.
     43 │         accel-profile flat
        ·                       ──┬─
        ·                         ╰── unexpected identifier
     44 │     }
        ╰────
      help: consider enclosing in double quotes ".."

> picky about syntax. I.e.: single word string MUST be quoted.

Seems like the opposite:

Example from kdl website without quotes

package { name my-pkg

Example from scfg with quotes

train "Shinkansen" {