public StringToken(LeftQuote leftQuote, Characters value, RightQuote rightQuote)
     : base(leftQuote, value, rightQuote)
 {
     this.leftQuote = leftQuote;
     this.value = value;
     this.rightQuote = rightQuote;
 }
 protected virtual Characters VisitCharacters(Characters node)
 {
     return VisitSyntaxNode(node) as Characters;
 }
 protected override Characters VisitCharacters(Characters node)
 {
     visitedCharacters = true;
     Assert.IsTrue(node.Value == "Property");
     return base.VisitCharacters(node);
 }