Is "first" underdefined in the CommonMark spec?

Spec
3

The spec should also consider now that there may be implicit link targets in the future. Probably, an explicit target overwrites an implicit one.

# Link Target

Here’s a [link][Link Target].

  [Link Target]: #first
  [Link Target]: #second

Here it is again: [link][Link Target].

  [Link Target]: #third

And a final time, [link][Link Target].

Most implementations choose #third. → Babelmark test