1. This can be a breaking change, if someone analyze message.
2. I don't like format (x:y) - message become unclear for users.

Could you explain reasons for this PR?

1. Sure. But is it a big deal? We could say the same thing if a sentence would have been reworded.
2. This is the format adopted by babel

The reason behind this change is cosmetic. I have built a tool to format YAML files and errors are handled this way:

try {
  data = yaml.load(contents)
} catch (e) {
  const line = e.mark.line + 1
  const column = e.mark.column + 1
  console.error(`${e.name}: ${e.reason} (${line}:${column})\n`)
  console.error(codeFrame(contents, line, column))
  process.exit(1)
}

The goal is to be able to switch to compact mode to prevent the code frame from being displayed but keeping the mark concise:

• Using YAMLException#toString() dumps code 👎
• Using YAMLException#toString(true) hides location 👎

Modifying Mark#toString(true) to be less verbose and adding it to YAMLException's compact output could be a good tradeoff between debugging info and length.

Let's keep this open, to revisit on major version bump.

Fixed in a58d8bc (together with stylus-like exception formatting).