anchor.diff:  /// because it does not have a unique value type.
   ///
   /// Example:
  +///
   ///     var encoder = new TomlEncoder();
   ///     encoder.encode({'a': [1, '2']});
  +///
   /// throws an [MixedArrayTypesError] because `1` and `'2'` are of different
   /// types.
   class MixedArrayTypesError {
  
positive.code: /// a table.
  ///
  /// Example:
  ///     [a]
  ///     b = 1
  ///
  ///     [a.b.c]
  ///     d = 2
  /// throws a [NotATableError] because `a.b.c` fails to create a sub-table of
  /// `a.b` which is an integer rather than not a table.
  class NotATableError {
  
negative.code: /// string which cannot be represented by TOML.
  class InvalidStringError {
  
    /// A message which describes the error.
    final String msg;
  
    InvalidStringError(this.msg);
  