/// <summary>
 /// Create a new <Leave/> element and append it as a child of this element.
 /// </summary>
 public VoiceResponse Leave()
 {
     var newChild = new Leave();
     this.Append(newChild);
     return this;
 }
 public VoiceResponse Leave(Leave leave)
 {
     this.Append(leave);
     return this;
 }