var str3 = '''Multi  Line  String''';  print( str3.splitMapJoin(      RegExp(r'^', multiLine: true), // Matches the beginning of the line      onMatch: (m) => '** ${m.group(0)}', // Adds asterisk to match      onNonMatch: (n) => n // Just return non-matches  ) ); /*** Multi**   Line**   String*/