Validation along token stack feature, C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        private const string tokenPrefix = " x ";
        
        public static void Main(string[] args)
        {
            var itemA = new Item() { Quantity = 1, ObjectId = "Normal Token x 1" };
            var itemB = new Item() { Quantity = 2, ObjectId = "Normal Token x 2" };
            var itemC = new Item() { Quantity = 3, ObjectId = "Rare Token x 3" };
            
            Handle(itemA, itemB);
            Handle(itemA, itemC);
            Handle(itemB, itemC);
        }
        
        private static void Handle(Item itemA, Item itemB) {
            var prefix = string.Empty;
            if (ValidateStackable(itemA, itemB, ref prefix)) {
                StackWrite(itemA.ObjectId, itemB.ObjectId, true);
                ResultWrite(itemA, itemB, prefix);
            }
            else StackWrite(itemA.ObjectId, itemB.ObjectId, false);
        }
        
        private static void StackWrite(string a, string b, bool stackable) {
            Write(string.Format("'{0}' {1} stack with '{2}'!", a, stackable ? "can" : "cannot", b));
        }
        
        private static void ResultWrite(Item itemA, Item itemB, string prefix) {
            Write(string.Format("'{0}'({1}) stacked with '{2}'({3}) results in '{4}'({5}).\n"
                                , itemA.ObjectId, itemA.Quantity.ToString(), itemB.ObjectId, itemB.Quantity.ToString()
                                , prefix, (itemA.Quantity + itemB.Quantity).ToString()));
        }
        
        private static void Write(string message) { Console.WriteLine(message); }
        
        private static bool ValidateStackable(Item itemA, Item itemB, ref string prefix) {
            return itemA.Quantity > 0 && itemB.Quantity > 0
                && IsSameKindOfItem(itemA, itemB, ref prefix);
        }
        
        private static bool IsSameKindOfItem(Item itemA, Item itemB, ref string prefix) {
            var itemAObjId = itemA.ObjectId;
            var itemBObjId = itemB.ObjectId;

if (itemAObjId.Contains(tokenPrefix) && itemBObjId.Contains(tokenPrefix))
            {
                var itemAPrefix = itemAObjId.IndexOf(tokenPrefix);
                var itemBPrefix = itemBObjId.IndexOf(tokenPrefix);
                var itemAName = itemAObjId.Substring(0, itemAPrefix);
                var itemBName = itemBObjId.Substring(0, itemBPrefix);
                var result = itemAName == itemBName;
                
                if (result) prefix = itemAName;
                else prefix = "invalid";
                
                return result;
            }
            else return false;
        }
    }
    
    public class Item {
        public int Quantity;
        public string ObjectId;
    }
}

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