toString method
A string representation of this object.
Some classes have a default textual representation,
often paired with a static parse function (like int.parse).
These classes will provide the textual representation as
their string representation.
Other classes have no meaningful textual representation
that a program will care about.
Such classes will typically override toString to provide
useful information when inspecting the object,
mainly for debugging or logging.
Implementation
@override
String toString() {
  String body = (_display_name != null && _display_name!.length > 0)
      ? '"${_quote(_display_name!)}" '
      : '';
  body += '<${_uri.toString()}>';
  _parameters!.forEach((dynamic key, dynamic value) {
    if (_parameters!.containsKey(key)) {
      body += ';$key';
      if (value != null) {
        body += '=$value';
      }
    }
  });
  return body;
}