diff --git a/Implab.Format.Test/JsonTests.cs b/Implab.Format.Test/JsonTests.cs
--- a/Implab.Format.Test/JsonTests.cs
+++ b/Implab.Format.Test/JsonTests.cs
@@ -9,8 +9,8 @@ using System.IO;
 
 namespace Implab.Format.Test {
     [TestFixture]
-    public class JsonTests {
-        
+    public class JsonTests {
+
         [Test]
         public void TestScannerValidTokens() {
             using (var scanner = JsonStringScanner.Create(@"9123, -123, 0, 0.1, -0.2, -0.1e3, 1.3E-3, ""some \t\n\u0020 text"", literal []{}:")) {
@@ -114,10 +114,36 @@ namespace Implab.Format.Test {
             DumpJsonParse("[{\"info\": [7,8,9]}]");
             DumpJsonFlatParse("[1,2,\"\",[3,4],{\"info\": [5,6]},{\"num\": [7,8,null]}, null,[null]]");
         }
-        
+
+        [Test]
+        public void JsonBenchmark() {
+            var t = Environment.TickCount;
+            using (var reader = new JsonXmlReader(JsonReader.Create("e:\\citylots.json"), new JsonXmlReaderOptions { NamespaceUri = "XmlReaderSimpleTest", RootName = "data" })) {
+                while (reader.Read()) {
+                }
+            }
+            Console.WriteLine($"JsonXmlReader: {Environment.TickCount - t} ms");
+
+            t = Environment.TickCount;
+            using(var reader = JsonReader.Create("e:\\citylots.json")) {
+                while(reader.Read()) {
+                }
+            }
+
+            Console.WriteLine($"JsonReader: {Environment.TickCount - t} ms");
+
+            t = Environment.TickCount;
+            using (var reader = XmlReader.Create("file:///e:\\citylots.xml")) {
+                while (reader.Read()) {
+                }
+            }
+
+            Console.WriteLine($"XmlReader: {Environment.TickCount - t} ms");
+        }
+
         void AssertRead(XmlReader reader, XmlNodeType expected) {
             Assert.IsTrue(reader.Read());
-            Console.WriteLine($"{new string(' ', reader.Depth*2)}{reader}");
+            Console.WriteLine($"{new string(' ', reader.Depth * 2)}{reader}");
             Assert.AreEqual(expected, reader.NodeType);
         }
 
diff --git a/Implab.Playground/Program.cs b/Implab.Playground/Program.cs
--- a/Implab.Playground/Program.cs
+++ b/Implab.Playground/Program.cs
@@ -78,103 +78,13 @@ namespace Implab.Playground {
 
         static void Main(string[] args) {
 
-            //var queue = new ConcurrentQueue<int>();
-            var queue = new AsyncQueue<int>();
-            //var queue = new SimpleAsyncQueue<int>();
-
-            const int wBatch = 32;
-            const long wCount = 1000000;
-            const long total = wBatch * wCount * 3;
-
-            long r1 = 0, r2 = 0, r3 = 0;
-            const int rBatch = 1000;
-            long read = 0;
-
-            var t1 = Environment.TickCount;
-
-            AsyncPool.RunThread(
-                () => {
-                    var buffer = new int[wBatch];
-                    for (int i = 0; i < wBatch; i++)
-                        buffer[i] = 1;
-
-                    for (int i = 0; i < wCount; i++)
-                        EnqueueRange(queue, buffer, 0, wBatch);
-                    Console.WriteLine("done writer #1: {0} ms", Environment.TickCount - t1);
-                },
-                () => {
-                    var buffer = new int[wBatch];
-                    for (int i = 0; i < wBatch; i++)
-                        buffer[i] = 1;
-
-                    for (int i = 0; i < wCount; i++)
-                        EnqueueRange(queue, buffer, 0, wBatch);
-                    Console.WriteLine("done writer #2: {0} ms", Environment.TickCount - t1);
-                },
-                () => {
-                    var buffer = new int[wBatch];
-                    for (int i = 0; i < wBatch; i++)
-                        buffer[i] = 1;
-
-                    for (int i = 0; i < wCount; i++)
-                        EnqueueRange(queue, buffer, 0, wBatch);
-                    Console.WriteLine("done writer #3: {0} ms", Environment.TickCount - t1);
-                },
-                () => {
-                    var buffer = new int[rBatch];
-
-                    while (read < total) {
-                        int actual;
-                        if (TryDequeueRange(queue, buffer, 0, rBatch, out actual)) {
-                            for (int i = 0; i < actual; i++)
-                                r1 += buffer[i];
-                            Interlocked.Add(ref read, actual);
-                        }
-                    }
-
-                    Console.WriteLine("done reader #1: {0} ms", Environment.TickCount - t1);
-                }/*,
-                () => {
-                    var buffer = new int[rBatch];
-
-                    while (read < total) {
-                        int actual;
-                        if (TryDequeueRange(queue, buffer, 0, rBatch, out actual)) {
-                            for (int i = 0; i < actual; i++)
-                                r2 += buffer[i];
-                            Interlocked.Add(ref read, actual);
-                        }
-                    }
-
-                    Console.WriteLine("done reader #2: {0} ms", Environment.TickCount - t1);
-                }*//*,
-                () => {
-                    var buffer = new int[rBatch];
-
-                    while (read < total) {
-                        int actual;
-                        if (TryDequeueRange(queue, buffer, 0, rBatch, out actual)) {
-                            for (int i = 0; i < actual; i++)
-                                r3 += buffer[i];
-                            Interlocked.Add(ref read, actual);
-                        }
-                    }
-
-                    Console.WriteLine("done reader #3: {0} ms", Environment.TickCount - t1);
-                }*/
-            )
-                .PromiseAll()
-                .Join();
-
-
-            Console.WriteLine(
-                "done: {0} ms, summ#1: {1}, summ#2: {2}, total: {3}, count: {4}",
-                Environment.TickCount - t1,
-                r1,
-                r2,
-                r1 + r2 + r3,
-                total
-            );
+            var t = Environment.TickCount;
+            using (var reader = JsonReader.Create("e:\\citylots.json")) {
+                while (reader.Read()) {
+                }
+            }
+
+            Console.WriteLine($"JsonReader: {Environment.TickCount - t} ms");
 
             Console.WriteLine("done");
         }
diff --git a/Implab/Automaton/AutomatonConst.cs b/Implab/Automaton/AutomatonConst.cs
--- a/Implab/Automaton/AutomatonConst.cs
+++ b/Implab/Automaton/AutomatonConst.cs
@@ -1,9 +1,9 @@
 
 namespace Implab.Automaton {
     public static class AutomatonConst {
-        public const int UNREACHABLE_STATE = -1;
+        public const int UnreachableState = -1;
 
-        public const int UNCLASSIFIED_INPUT = 0;
+        public const int UnclassifiedInput = 0;
     }
 }
 
diff --git a/Implab/Automaton/DFATable.cs b/Implab/Automaton/DFATable.cs
--- a/Implab/Automaton/DFATable.cs
+++ b/Implab/Automaton/DFATable.cs
@@ -116,7 +116,7 @@ namespace Implab.Automaton {
 
             for (int i = 0; i < StateCount; i++)
                 for (int j = 0; j < AlphabetSize; j++)
-                    table[i, j] = AutomatonConst.UNREACHABLE_STATE;
+                    table[i, j] = AutomatonConst.UnreachableState;
 
             foreach (var t in this)
                 table[t.s1,t.edge] = (byte)t.s2;
@@ -290,11 +290,11 @@ namespace Implab.Automaton {
 
             var nextCls = 0;
             foreach (var item in minClasses) {
-                if (nextCls == AutomatonConst.UNCLASSIFIED_INPUT)
+                if (nextCls == AutomatonConst.UnclassifiedInput)
                     nextCls++;
 
                 // сохраняем DFAConst.UNCLASSIFIED_INPUT
-                var cls = item.Contains(AutomatonConst.UNCLASSIFIED_INPUT) ? AutomatonConst.UNCLASSIFIED_INPUT : nextCls++;
+                var cls = item.Contains(AutomatonConst.UnclassifiedInput) ? AutomatonConst.UnclassifiedInput : nextCls++;
                 optimalDFA.AddSymbol(cls);
 
                 foreach (var a in item)
@@ -326,7 +326,7 @@ namespace Implab.Automaton {
                 data.Add(String.Format(
                     "{0} -> {2} [label={1}];",
                     String.Join("", stateAlphabet.GetSymbols(t.s1)),
-                    ToLiteral(ToLiteral(String.Join("", t.edge == AutomatonConst.UNCLASSIFIED_INPUT ? new [] { "@" } : inputAlphabet.GetSymbols(t.edge).Select(x => x.ToString())))),
+                    ToLiteral(ToLiteral(String.Join("", t.edge == AutomatonConst.UnclassifiedInput ? new [] { "@" } : inputAlphabet.GetSymbols(t.edge).Select(x => x.ToString())))),
                     String.Join("", stateAlphabet.GetSymbols(t.s2))
                 ));
             data.Add("}");
diff --git a/Implab/Automaton/MapAlphabet.cs b/Implab/Automaton/MapAlphabet.cs
--- a/Implab/Automaton/MapAlphabet.cs
+++ b/Implab/Automaton/MapAlphabet.cs
@@ -54,7 +54,7 @@ namespace Implab.Automaton {
                 return cls;
             if (!m_supportUnclassified)
                 throw new ArgumentOutOfRangeException("symbol", "The specified symbol isn't in the alphabet");
-            return AutomatonConst.UNCLASSIFIED_INPUT;
+            return AutomatonConst.UnclassifiedInput;
         }
 
         public int Count {
diff --git a/Implab/Automaton/RegularExpressions/RegularExpressionVisitor.cs b/Implab/Automaton/RegularExpressions/RegularExpressionVisitor.cs
--- a/Implab/Automaton/RegularExpressions/RegularExpressionVisitor.cs
+++ b/Implab/Automaton/RegularExpressions/RegularExpressionVisitor.cs
@@ -129,7 +129,7 @@ namespace Implab.Automaton.RegularExpres
             if (m_root == null)
                 m_root = token;
             m_idx++;
-            m_indexes[m_idx] = AutomatonConst.UNCLASSIFIED_INPUT;
+            m_indexes[m_idx] = AutomatonConst.UnclassifiedInput;
             m_firstpos = new HashSet<int>(new[] { m_idx });
             m_lastpos = new HashSet<int>(new[] { m_idx });
             Followpos(m_idx);
diff --git a/Implab/Formats/CharAlphabet.cs b/Implab/Formats/CharAlphabet.cs
--- a/Implab/Formats/CharAlphabet.cs
+++ b/Implab/Formats/CharAlphabet.cs
@@ -4,7 +4,7 @@ using Implab.Automaton;
 using System;
 
 namespace Implab.Formats {
-    public class CharAlphabet: IndexedAlphabetBase<char> {
+    public class CharAlphabet : IndexedAlphabetBase<char> {
 
         public override int GetSymbolIndex(char symbol) {
             return symbol;
diff --git a/Implab/Formats/CharMap.cs b/Implab/Formats/CharMap.cs
--- a/Implab/Formats/CharMap.cs
+++ b/Implab/Formats/CharMap.cs
@@ -25,7 +25,7 @@ namespace Implab.Formats {
         }
 
         public bool Contains(char symbol) {
-            return symbol >= m_min && symbol <= m_max && m_map[symbol-m_min] != AutomatonConst.UNCLASSIFIED_INPUT;
+            return symbol >= m_min && symbol <= m_max && m_map[symbol-m_min] != AutomatonConst.UnclassifiedInput;
         }
 
         public IEnumerable<char> GetSymbols(int cls) {
@@ -36,7 +36,7 @@ namespace Implab.Formats {
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public int Translate(char symbol) {
-            return symbol >= m_min && symbol <= m_max ? m_map[symbol-m_min] : AutomatonConst.UNCLASSIFIED_INPUT;
+            return symbol >= m_min && symbol <= m_max ? m_map[symbol-m_min] : AutomatonConst.UnclassifiedInput;
         }
     }
 }
diff --git a/Implab/Formats/Grammar.cs b/Implab/Formats/Grammar.cs
--- a/Implab/Formats/Grammar.cs
+++ b/Implab/Formats/Grammar.cs
@@ -16,7 +16,7 @@ namespace Implab.Formats {
         }
 
         protected SymbolToken UnclassifiedToken() {
-            return new SymbolToken(AutomatonConst.UNCLASSIFIED_INPUT);
+            return new SymbolToken(AutomatonConst.UnclassifiedInput);
         }
 
         protected void DefineAlphabet(IEnumerable<TSymbol> alphabet) {
@@ -42,7 +42,7 @@ namespace Implab.Formats {
 
         int TranslateOrAdd(TSymbol ch) {
             var t = AlphabetBuilder.Translate(ch);
-            if (t == AutomatonConst.UNCLASSIFIED_INPUT)
+            if (t == AutomatonConst.UnclassifiedInput)
                 t = AlphabetBuilder.DefineSymbol(ch);
             return t;
         }
@@ -53,7 +53,7 @@ namespace Implab.Formats {
 
         int TranslateOrDie(TSymbol ch) {
             var t = AlphabetBuilder.Translate(ch);
-            if (t == AutomatonConst.UNCLASSIFIED_INPUT)
+            if (t == AutomatonConst.UnclassifiedInput)
                     throw new ApplicationException(String.Format("Symbol '{0}' is UNCLASSIFIED", ch));
             return t;
         }
diff --git a/Implab/Formats/InputScanner.cs b/Implab/Formats/InputScanner.cs
--- a/Implab/Formats/InputScanner.cs
+++ b/Implab/Formats/InputScanner.cs
@@ -69,7 +69,7 @@ namespace Implab.Formats {
 
             while(offset < max) {
                 next = m_dfa[next, m_alphabet.Translate(data[offset])];
-                if (next == AutomatonConst.UNREACHABLE_STATE) {
+                if (next == AutomatonConst.UnreachableState) {
                     // scanner stops on the next position after last recognized symbol
                     m_position = offset;
                     return false;
diff --git a/Implab/Formats/Json/JsonGrammar.cs b/Implab/Formats/Json/JsonGrammar.cs
--- a/Implab/Formats/Json/JsonGrammar.cs
+++ b/Implab/Formats/Json/JsonGrammar.cs
@@ -31,8 +31,8 @@ namespace Implab.Formats.Json {
             get { return _instance.Value; }
         }
 
-        readonly InputScanner<TokenType> m_jsonExpression;
-        readonly InputScanner<TokenType> m_stringExpression;
+        readonly FastInputScanner<TokenType> m_jsonExpression;
+        readonly FastInputScanner<TokenType> m_stringExpression;
         readonly CharAlphabet m_defaultAlphabet = new CharAlphabet();
 
         public CharAlphabet DefaultAlphabet { get { return m_defaultAlphabet; } }
@@ -87,15 +87,15 @@ namespace Implab.Formats.Json {
                 .Or(unescaped.Closure().Tag(TokenType.UnescapedChar));
                     
 
-            m_jsonExpression = BuildScanner(jsonExpression);
-            m_stringExpression = BuildScanner(jsonStringExpression);
+            m_jsonExpression = BuildFastScanner(jsonExpression);
+            m_stringExpression = BuildFastScanner(jsonStringExpression);
         }
 
-        public static InputScanner<TokenType> CreateJsonExpressionScanner() {
+        public static FastInputScanner<TokenType> CreateJsonExpressionScanner() {
             return Instance.m_jsonExpression.Clone();
         }
 
-        public static InputScanner<TokenType> CreateStringExpressionScanner() {
+        public static FastInputScanner<TokenType> CreateStringExpressionScanner() {
             return Instance.m_stringExpression.Clone();
         }
 
@@ -109,7 +109,7 @@ namespace Implab.Formats.Json {
             return SymbolToken(Enumerable.Range(start, stop - start + 1).Select(x => (char)x));
         }
 
-        public InputScanner<TokenType> BuildScanner(Token regexp) {
+        public FastInputScanner<TokenType> BuildFastScanner(Token regexp) {
             var dfa = new RegularDFA<char, TokenType>(AlphabetBuilder);
 
             var visitor = new RegularExpressionVisitor<TokenType>(dfa);
@@ -122,12 +122,12 @@ namespace Implab.Formats.Json {
             var ab = new CharAlphabet();
             var optimal = dfa.Optimize(ab);
 
-            return new InputScanner<TokenType>(
+            return new FastInputScanner<TokenType>(
                 optimal.CreateTransitionTable(),
                 optimal.CreateFinalStateTable(),
                 NormalizeTags(optimal.CreateTagTable()),
                 optimal.InitialState,
-                ab.CreateCharMap()
+                ab.GetTranslationMap()
             );
         }
 
diff --git a/Implab/Formats/Json/JsonReader.cs b/Implab/Formats/Json/JsonReader.cs
--- a/Implab/Formats/Json/JsonReader.cs
+++ b/Implab/Formats/Json/JsonReader.cs
@@ -48,7 +48,7 @@ namespace Implab.Formats.Json {
 
             public bool Move(JsonTokenType token) {
                 var next = m_dfa[m_state, (int)token];
-                if (next == AutomatonConst.UNREACHABLE_STATE)
+                if (next == AutomatonConst.UnreachableState)
                     return false;
                 m_state = next;
                 return true;
@@ -116,7 +116,7 @@ namespace Implab.Formats.Json {
         MemberContext m_memberContext = MemberContext.MemberValue;
 
         JsonElementType m_elementType;
-        object m_elementValue;
+        string m_elementValue;
         string m_memberName = String.Empty;
 
         Stack<ParserContext> m_stack = new Stack<ParserContext>();
@@ -152,7 +152,7 @@ namespace Implab.Formats.Json {
         /// <summary>
         /// Значение элемента. Только для элементов типа <see cref="JsonElementType.Value"/>, для остальных <c>null</c>
         /// </summary>
-        public object ElementValue {
+        public string ElementValue {
             get { return m_elementValue; }
         }
 
@@ -213,11 +213,11 @@ namespace Implab.Formats.Json {
                         return true;
                     case JsonTokenType.Number:
                         m_elementType = JsonElementType.Value;
-                        m_elementValue = double.Parse(tokenValue, CultureInfo.InvariantCulture);
+                        m_elementValue = tokenValue;
                         return true;
                     case JsonTokenType.Literal:
                         m_elementType = JsonElementType.Value;
-                        m_elementValue = ParseLiteral(tokenValue);
+                        m_elementValue = tokenValue == "null" ? null : tokenValue;
                         return true;
                     case JsonTokenType.NameSeparator:
                         m_memberContext = MemberContext.MemberValue;
diff --git a/Implab/Formats/Json/JsonScanner.cs b/Implab/Formats/Json/JsonScanner.cs
--- a/Implab/Formats/Json/JsonScanner.cs
+++ b/Implab/Formats/Json/JsonScanner.cs
@@ -10,8 +10,8 @@ namespace Implab.Formats.Json {
     /// Сканнер (лексер), разбивающий поток символов на токены JSON.
     /// </summary>
     public abstract class JsonScanner : Disposable {
-        readonly InputScanner<JsonGrammar.TokenType> m_jsonContext = JsonGrammar.CreateJsonExpressionScanner();
-        readonly InputScanner<JsonGrammar.TokenType> m_stringContext = JsonGrammar.CreateStringExpressionScanner();
+        readonly FastInputScanner<JsonGrammar.TokenType> m_jsonContext = JsonGrammar.CreateJsonExpressionScanner();
+        readonly FastInputScanner<JsonGrammar.TokenType> m_stringContext = JsonGrammar.CreateStringExpressionScanner();
 
         readonly char[] m_unescapeBuf = new char[4];
         readonly char[] m_buffer;
@@ -25,7 +25,7 @@ namespace Implab.Formats.Json {
             m_length = length;
         }
 
-        bool ReadChunk(InputScanner<JsonGrammar.TokenType> scanner, out JsonGrammar.TokenType tokenType) {
+        bool ReadChunk(FastInputScanner<JsonGrammar.TokenType> scanner, out JsonGrammar.TokenType tokenType) {
             scanner.ResetState();
 
             while(scanner.Scan(m_buffer, m_pos, m_length)) {
@@ -71,7 +71,7 @@ namespace Implab.Formats.Json {
             return true;
         }
 
-        bool ReadStringChunk(InputScanner<JsonGrammar.TokenType> scanner, out JsonGrammar.TokenType tokenType) {
+        bool ReadStringChunk(FastInputScanner<JsonGrammar.TokenType> scanner, out JsonGrammar.TokenType tokenType) {
             scanner.ResetState();
 
             while (scanner.Scan(m_buffer, m_pos, m_length)) {
@@ -107,7 +107,7 @@ namespace Implab.Formats.Json {
 
             // scanner stops as scannerPos
             if (!scanner.IsFinal)
-                throw new ParserException($"Unexpected character '{m_buffer[scannerPos + 1]}'");
+                throw new ParserException($"Unexpected character '{m_buffer[scannerPos]}'");
 
             if (scannerPos != m_pos) {
                 m_tokenBuilder.Append(m_buffer, m_pos, scannerPos - m_pos);
diff --git a/Implab/Implab.csproj b/Implab/Implab.csproj
--- a/Implab/Implab.csproj
+++ b/Implab/Implab.csproj
@@ -55,6 +55,7 @@
     <Compile Include="Diagnostics\TraceEventType.cs" />
     <Compile Include="Diagnostics\TraceSourceAttribute.cs" />
     <Compile Include="Formats\CharMap.cs" />
+    <Compile Include="Formats\FastInpurScanner.cs" />
     <Compile Include="Formats\InputScanner.cs" />
     <Compile Include="Formats\Json\JsonStringScanner.cs" />
     <Compile Include="Formats\Json\JsonTextScanner.cs" />
diff --git a/Implab/Xml/JsonXmlReader.cs b/Implab/Xml/JsonXmlReader.cs
--- a/Implab/Xml/JsonXmlReader.cs
+++ b/Implab/Xml/JsonXmlReader.cs
@@ -39,7 +39,7 @@ namespace Implab.Xml {
         int m_xmlDepth;
 
         XmlSimpleAttribute[] m_attributes;
-        object m_value;
+        string m_value;
         bool m_isEmpty;
 
         XmlNodeType m_nodeType = XmlNodeType.None;
@@ -158,29 +158,13 @@ namespace Implab.Xml {
 
         public override string Value {
             get {
-                return ConvertValueToString(m_value);
+                return m_value;
             }
         }
-
-        static string ConvertValueToString(object value) {
-            if (value == null)
-                return string.Empty;
-
-            switch (Convert.GetTypeCode(value)) {
-                case TypeCode.Double:
-                    return ((double)value).ToString(CultureInfo.InvariantCulture);
-                case TypeCode.String:
-                    return (string)value;
-                case TypeCode.Boolean:
-                    return (bool)value ? "true" : "false";
-                default:
-                    return value.ToString();
-            }
-        }
-
+        
         public override string GetAttribute(int i) {
             Safe.ArgumentInRange(i, 0, AttributeCount - 1, nameof(i));
-            return ConvertValueToString(m_attributes[i].Value);
+            return m_attributes[i].Value;
         }
 
         public override string GetAttribute(string name) {
@@ -188,7 +172,7 @@ namespace Implab.Xml {
                 return null;
             var qName = m_context.Resolve(name);
             var attr = Array.Find(m_attributes, x => x.QName == qName);
-            var value = ConvertValueToString(attr?.Value);
+            var value = attr?.Value;
             return value == string.Empty ? null : value;
         }
 
@@ -197,7 +181,7 @@ namespace Implab.Xml {
                 return null;
             var qName = new XmlQualifiedName(name, namespaceURI);
             var attr = Array.Find(m_attributes, x => x.QName == qName);
-            var value = ConvertValueToString(attr?.Value);
+            var value = attr?.Value;
             return value == string.Empty ? null : value;
         }
 
@@ -319,7 +303,7 @@ namespace Implab.Xml {
             }
         }
 
-        void ValueNode(object value) {
+        void ValueNode(string value) {
             if (!IsSibling()) // the node is nested
                 m_xmlDepth++;
 
@@ -344,11 +328,11 @@ namespace Implab.Xml {
                     if (attr.QName.Name == "xmlns") {
                         if (context == m_context)
                              context = new XmlNameContext(m_context, m_xmlDepth);
-                        context.DefinePrefix(ConvertValueToString(attr.Value), string.Empty);
+                        context.DefinePrefix(attr.Value, string.Empty);
                     } else if (attr.Prefix == m_xmlnsPrefix) {
                         if (context == m_context)
                             context = new XmlNameContext(m_context, m_xmlDepth);
-                        context.DefinePrefix(ConvertValueToString(attr.Value), attr.QName.Name);
+                        context.DefinePrefix(attr.Value, attr.QName.Name);
                     } else {
                         string attrPrefix;
                         if (string.IsNullOrEmpty(attr.QName.Namespace))
@@ -516,7 +500,7 @@ namespace Implab.Xml {
                                     m_jsonValueName,
                                     m_jsonNamespace,
                                     new[] {
-                                        new XmlSimpleAttribute("nil", m_xsiNamespace, m_xsiPrefix, true)
+                                        new XmlSimpleAttribute("nil", m_xsiNamespace, m_xsiPrefix, "true")
                                     },
                                     true
                                 );
@@ -607,7 +591,7 @@ namespace Implab.Xml {
         public override string ToString() {
             switch (NodeType) {
                 case XmlNodeType.Element:
-                    return $"<{Name} {string.Join(" ", (m_attributes ?? new XmlSimpleAttribute[0]).Select(x => $"{x.Prefix}{(string.IsNullOrEmpty(x.Prefix) ? "" : ":")}{x.QName.Name}='{ConvertValueToString(x.Value)}'"))} {(IsEmptyElement ? "/" : "")}>";
+                    return $"<{Name} {string.Join(" ", (m_attributes ?? new XmlSimpleAttribute[0]).Select(x => $"{x.Prefix}{(string.IsNullOrEmpty(x.Prefix) ? "" : ":")}{x.QName.Name}='{x.Value}'"))} {(IsEmptyElement ? "/" : "")}>";
                 case XmlNodeType.Attribute:
                     return $"@{Name}";
                 case XmlNodeType.Text:
diff --git a/Implab/Xml/XmlSimpleAttribute.cs b/Implab/Xml/XmlSimpleAttribute.cs
--- a/Implab/Xml/XmlSimpleAttribute.cs
+++ b/Implab/Xml/XmlSimpleAttribute.cs
@@ -7,7 +7,7 @@ using System.Xml;
 
 namespace Implab.Xml {
     public class XmlSimpleAttribute {
-        public XmlSimpleAttribute(string name, string ns, string prefix, object value) {
+        public XmlSimpleAttribute(string name, string ns, string prefix, string value) {
             QName = new XmlQualifiedName(name, ns);
             Prefix = prefix;
             Value = value;
@@ -17,6 +17,6 @@ namespace Implab.Xml {
 
         public string Prefix { get; set; }
 
-        public object Value { get; set; }
+        public string Value { get; set; }
     }
 }