Root @ 0..16
  SimpleMessage @ 0..16
    Pattern @ 0..16
      Placeholder @ 0..16
        FunctionExpression @ 0..16
          TOKEN LeftBraceToken @ 0..1 "{"
          Function @ 1..15
            TOKEN ColonToken @ 1..2 ":"
            Identifier @ 2..4
              TOKEN NameToken @ 2..4 "fn"
            Option @ 5..15
              Identifier @ 5..9
                TOKEN NameToken @ 5..8 "opt"
                TOKEN ColonToken @ 8..9 ":"
                Missing @ 9..9
              TOKEN EqualsToken @ 9..10 "="
              UnquotedLiteral @ 10..15
                TOKEN NameToken @ 10..15 "value"
          TOKEN RightBraceToken @ 15..16 "}"
--diagnostics--
MissingIdentifierName @ 8..9 (line 1, col 9): missing identifier name after ':'
