File: XPathNavigator.cs

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//------------------------------------------------------------------------------
// <copyright file="XPathNavigator.cs" company="Microsoft">
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// </copyright>
// <owner current="true" primary="true">Microsoft</owner>
//------------------------------------------------------------------------------

using System.ComponentModel;
using System.IO;
using System.Collections;
using System.Collections.Generic;
using System.Globalization;
using System.Xml.Schema;
using System.Diagnostics;
using System.Diagnostics.Contracts;
using System.Security;
using System.Security.Policy;
using System.Security.Permissions;
using System.Text;
using System.Xml;
using MS.Internal.Xml.Cache;
using MS.Internal.Xml.XPath;

namespace System.Xml.XPath {
    // Provides a navigation interface API using XPath data model.
    [DebuggerDisplay("{debuggerDisplayProxy}")]
#if CONTRACTS_FULL
    [ContractClass(typeof(XPathNavigatorContract))]
#endif
    public abstract class XPathNavigator : XPathItem, ICloneable, IXPathNavigable, IXmlNamespaceResolver {
        internal static readonly XPathNavigatorKeyComparer comparer = new XPathNavigatorKeyComparer();

        //-----------------------------------------------
        // Object
        //-----------------------------------------------

        public override string ToString() {
            return Value;
        }

        //-----------------------------------------------
        // XPathItem
        //-----------------------------------------------

        public override sealed bool IsNode {
            get { return true; }
        }

        public override XmlSchemaType XmlType {
            get {
                IXmlSchemaInfo schemaInfo = SchemaInfo;
                if (schemaInfo != null) {
                    if (schemaInfo.Validity == XmlSchemaValidity.Valid) {
                        XmlSchemaType memberType = schemaInfo.MemberType; 
                        if (memberType != null) {
                            return memberType; 
                        }
                        return schemaInfo.SchemaType;
                    }
                }
                return null;
            }
        }

        public virtual void SetValue(string value) {
            throw new NotSupportedException();
        }

        public override object TypedValue {
            get {
                IXmlSchemaInfo schemaInfo = SchemaInfo;
                XmlSchemaType schemaType;
                XmlSchemaDatatype datatype;
                if (schemaInfo != null) {
                    if (schemaInfo.Validity == XmlSchemaValidity.Valid) {
                        schemaType = schemaInfo.MemberType;
                        if (schemaType == null) {
                            schemaType = schemaInfo.SchemaType;
                        }
                        if (schemaType != null) {
                            datatype = schemaType.Datatype;
                            if (datatype != null) {
                                return schemaType.ValueConverter.ChangeType(Value, datatype.ValueType, this);
                            }
                        }
                    }
                    else {
                        schemaType = schemaInfo.SchemaType;
                        if (schemaType != null) {
                            datatype = schemaType.Datatype;
                            if (datatype != null) {
                                return schemaType.ValueConverter.ChangeType(datatype.ParseValue(Value, NameTable, this), datatype.ValueType, this);
                            }
                        }
                    }
                }
                return Value; 
            }
        }

        public virtual void SetTypedValue(object typedValue) {
            if (typedValue == null) {
                throw new ArgumentNullException("typedValue");
            }
            switch (NodeType) {
                case XPathNodeType.Element:
                case XPathNodeType.Attribute:
                    break;
                default:
                    throw new InvalidOperationException(Res.GetString(Res.Xpn_BadPosition));
            }
            string value = null; 
            IXmlSchemaInfo schemaInfo = SchemaInfo;
            if (schemaInfo != null) {
                XmlSchemaType schemaType = schemaInfo.SchemaType;
                if (schemaType != null) {
                    value = schemaType.ValueConverter.ToString(typedValue, this);
                    XmlSchemaDatatype datatype = schemaType.Datatype;
                    if (datatype != null) {
                        datatype.ParseValue(value, NameTable, this);
                    }
                }
            }
            if (value == null) {
                value = XmlUntypedConverter.Untyped.ToString(typedValue, this);
            }
            SetValue(value);
        }

        public override Type ValueType {
            get {
                IXmlSchemaInfo schemaInfo = SchemaInfo;
                XmlSchemaType schemaType;
                XmlSchemaDatatype datatype;
                if (schemaInfo != null) {
                    if (schemaInfo.Validity == XmlSchemaValidity.Valid) {
                        schemaType = schemaInfo.MemberType;
                        if (schemaType == null) {
                            schemaType = schemaInfo.SchemaType;
                        }
                        if (schemaType != null) {
                            datatype = schemaType.Datatype;
                            if (datatype != null) {
                                return datatype.ValueType;
                            }
                        }
                    }
                    else {
                        schemaType = schemaInfo.SchemaType;
                        if (schemaType != null) {
                            datatype = schemaType.Datatype;
                            if (datatype != null) {
                                return datatype.ValueType;
                            }
                        }
                    }
                }
                return typeof(string);
            }
        }

        public override bool ValueAsBoolean {
            get {
                IXmlSchemaInfo schemaInfo = SchemaInfo;
                XmlSchemaType schemaType;
                XmlSchemaDatatype datatype;
                if (schemaInfo != null) {
                    if (schemaInfo.Validity == XmlSchemaValidity.Valid) {
                        schemaType = schemaInfo.MemberType;
                        if (schemaType == null) {
                            schemaType = schemaInfo.SchemaType;
                        }
                        if (schemaType != null) {
                            return schemaType.ValueConverter.ToBoolean(Value);
                        }
                    }
                    else {
                        schemaType = schemaInfo.SchemaType;
                        if (schemaType != null) {
                            datatype = schemaType.Datatype;
                            if (datatype != null) {
                                return schemaType.ValueConverter.ToBoolean(datatype.ParseValue(Value, NameTable, this));
                            }
                        }
                    }
                }
                return XmlUntypedConverter.Untyped.ToBoolean(Value);
            }
        }

        public override DateTime ValueAsDateTime {
            get {
                IXmlSchemaInfo schemaInfo = SchemaInfo;
                XmlSchemaType schemaType;
                XmlSchemaDatatype datatype;
                if (schemaInfo != null) {
                    if (schemaInfo.Validity == XmlSchemaValidity.Valid) {
                        schemaType = schemaInfo.MemberType;
                        if (schemaType == null) {
                            schemaType = schemaInfo.SchemaType;
                        }
                        if (schemaType != null) {
                            return schemaType.ValueConverter.ToDateTime(Value);
                        }
                    }
                    else {
                        schemaType = schemaInfo.SchemaType;
                        if (schemaType != null) {
                            datatype = schemaType.Datatype;
                            if (datatype != null) {
                                return schemaType.ValueConverter.ToDateTime(datatype.ParseValue(Value, NameTable, this));
                            }
                        }
                    }
                }
                return XmlUntypedConverter.Untyped.ToDateTime(Value);
            }
        }

        public override double ValueAsDouble {
            get {
                IXmlSchemaInfo schemaInfo = SchemaInfo;
                XmlSchemaType schemaType;
                XmlSchemaDatatype datatype;
                if (schemaInfo != null) {
                    if (schemaInfo.Validity == XmlSchemaValidity.Valid) {
                        schemaType = schemaInfo.MemberType;
                        if (schemaType == null) {
                            schemaType = schemaInfo.SchemaType;
                        }
                        if (schemaType != null) {
                            return schemaType.ValueConverter.ToDouble(Value);
                        }
                    }
                    else {
                        schemaType = schemaInfo.SchemaType;
                        if (schemaType != null) {
                            datatype = schemaType.Datatype;
                            if (datatype != null) {
                                return schemaType.ValueConverter.ToDouble(datatype.ParseValue(Value, NameTable, this));
                            }
                        }
                    }
                }
                return XmlUntypedConverter.Untyped.ToDouble(Value);
            }
        }

        public override int ValueAsInt {
            get {
                IXmlSchemaInfo schemaInfo = SchemaInfo;
                XmlSchemaType schemaType;
                XmlSchemaDatatype datatype;
                if (schemaInfo != null) {
                    if (schemaInfo.Validity == XmlSchemaValidity.Valid) {
                        schemaType = schemaInfo.MemberType;
                        if (schemaType == null) {
                            schemaType = schemaInfo.SchemaType;
                        }
                        if (schemaType != null) {
                            return schemaType.ValueConverter.ToInt32(Value);
                        }
                    }
                    else {
                        schemaType = schemaInfo.SchemaType;
                        if (schemaType != null) {
                            datatype = schemaType.Datatype;
                            if (datatype != null) {
                                return schemaType.ValueConverter.ToInt32(datatype.ParseValue(Value, NameTable, this));
                            }
                        }
                    }
                }
                return XmlUntypedConverter.Untyped.ToInt32(Value);
            }
        }

        public override long ValueAsLong {
            get {
                IXmlSchemaInfo schemaInfo = SchemaInfo;
                XmlSchemaType schemaType;
                XmlSchemaDatatype datatype;
                if (schemaInfo != null) {
                    if (schemaInfo.Validity == XmlSchemaValidity.Valid) {
                        schemaType = schemaInfo.MemberType;
                        if (schemaType == null) {
                            schemaType = schemaInfo.SchemaType;
                        }
                        if (schemaType != null) {
                            return schemaType.ValueConverter.ToInt64(Value);
                        }
                    }
                    else {
                        schemaType = schemaInfo.SchemaType;
                        if (schemaType != null) {
                            datatype = schemaType.Datatype;
                            if (datatype != null) {
                                return schemaType.ValueConverter.ToInt64(datatype.ParseValue(Value, NameTable, this));
                            }
                        }
                    }
                }
                return XmlUntypedConverter.Untyped.ToInt64(Value);
            }
        }

        public override object ValueAs(Type returnType, IXmlNamespaceResolver nsResolver) {
            if (nsResolver == null) {
                nsResolver = this;
            }
            IXmlSchemaInfo schemaInfo = SchemaInfo;
            XmlSchemaType schemaType;
            XmlSchemaDatatype datatype;
            if (schemaInfo != null) {
                if (schemaInfo.Validity == XmlSchemaValidity.Valid) {
                    schemaType = schemaInfo.MemberType;
                    if (schemaType == null) {
                        schemaType = schemaInfo.SchemaType;
                    }
                    if (schemaType != null) {
                        return schemaType.ValueConverter.ChangeType(Value, returnType, nsResolver);
                    }
                }
                else {
                    schemaType = schemaInfo.SchemaType;
                    if (schemaType != null) {
                        datatype = schemaType.Datatype;
                        if (datatype != null) {
                            return schemaType.ValueConverter.ChangeType(datatype.ParseValue(Value, NameTable, nsResolver), returnType, nsResolver);
                        }
                    }
                }
            }
            return XmlUntypedConverter.Untyped.ChangeType(Value, returnType, nsResolver);
        }

        //-----------------------------------------------
        // ICloneable
        //-----------------------------------------------

        object ICloneable.Clone() {
            return Clone();
        }

        //-----------------------------------------------
        // IXPathNavigable
        //-----------------------------------------------

        public virtual XPathNavigator CreateNavigator() {
            return Clone();
        }

        //-----------------------------------------------
        // IXmlNamespaceResolver
        //-----------------------------------------------

        public abstract XmlNameTable NameTable { get; }

        public virtual string LookupNamespace(string prefix) {
            if (prefix == null)
                return null;

            if (NodeType != XPathNodeType.Element) {
                XPathNavigator navSave = Clone();

                // If current item is not an element, then try parent
                if (navSave.MoveToParent())
                    return navSave.LookupNamespace(prefix);
            }
            else if (MoveToNamespace(prefix)) {
                string namespaceURI = Value;
                MoveToParent();
                return namespaceURI;
            }

            // Check for "", "xml", and "xmlns" prefixes
            if (prefix.Length == 0)
                return string.Empty;
            else if (prefix == "xml")
                return XmlReservedNs.NsXml;
            else if (prefix == "xmlns")
                return XmlReservedNs.NsXmlNs;

            return null;
        }

        public virtual string LookupPrefix(string namespaceURI) {
            if (namespaceURI == null)
                return null;

            XPathNavigator navClone = Clone();

            if (NodeType != XPathNodeType.Element) {
                // If current item is not an element, then try parent
                if (navClone.MoveToParent())
                    return navClone.LookupPrefix(namespaceURI);
            }
            else {
                if (navClone.MoveToFirstNamespace(XPathNamespaceScope.All)) {
                    // Loop until a matching namespace is found
                    do {
                        if (namespaceURI == navClone.Value)
                            return navClone.LocalName;
                    }
                    while (navClone.MoveToNextNamespace(XPathNamespaceScope.All));
                }
            }

            // Check for default, "xml", and "xmlns" namespaces
            if (namespaceURI == LookupNamespace(string.Empty))
                return string.Empty;
            else if (namespaceURI == XmlReservedNs.NsXml)
                return "xml";
            else if (namespaceURI == XmlReservedNs.NsXmlNs)
                return "xmlns";

            return null;
        }

// This pragma disables a warning that the return type is not CLS-compliant, but generics are part of CLS in Whidbey. 
#pragma warning disable 3002
        public virtual IDictionary<string,string> GetNamespacesInScope(XmlNamespaceScope scope) {
#pragma warning restore 3002
            XPathNodeType nt = NodeType;
            if ((nt != XPathNodeType.Element && scope != XmlNamespaceScope.Local) || nt == XPathNodeType.Attribute || nt == XPathNodeType.Namespace) {
                XPathNavigator navSave = Clone();

                // If current item is not an element, then try parent
                if (navSave.MoveToParent())
                    return navSave.GetNamespacesInScope(scope);
            }

            Dictionary<string,string> dict = new Dictionary<string,string>();

            // "xml" prefix always in scope
            if (scope == XmlNamespaceScope.All)
                dict["xml"] = XmlReservedNs.NsXml;

            // Now add all in-scope namespaces
            if (MoveToFirstNamespace((XPathNamespaceScope) scope)) {
                do {
                    string prefix = LocalName;
                    string ns = Value;

                    // Exclude xmlns="" declarations unless scope = Local
                    if (prefix.Length != 0 || ns.Length != 0 || scope == XmlNamespaceScope.Local)
                        dict[prefix] = ns;
                }
                while (MoveToNextNamespace((XPathNamespaceScope) scope));

                MoveToParent();
            }

            return dict;
        }

        //-----------------------------------------------
        // XPathNavigator
        //-----------------------------------------------

        // Returns an object of type IKeyComparer. Using this the navigators can be hashed
        // on the basis of actual position it represents rather than the clr reference of 
        // the navigator object.
        public static IEqualityComparer NavigatorComparer {
            get { return comparer; }
        }

        public abstract XPathNavigator Clone();

        public abstract XPathNodeType NodeType { get; }

        public abstract string LocalName { get; }

        public abstract string Name { get; }

        public abstract string NamespaceURI { get; }

        public abstract string Prefix { get; }

        public abstract string BaseURI { get; }

        public abstract bool IsEmptyElement { get; }

        public virtual string XmlLang {
            get {
                XPathNavigator navClone = Clone();
                do {
                    if (navClone.MoveToAttribute("lang", XmlReservedNs.NsXml))
                        return navClone.Value;
                }
                while (navClone.MoveToParent());

                return string.Empty;
            }
        }

        public virtual XmlReader ReadSubtree() {
            switch (NodeType) {
                case XPathNodeType.Root:
                case XPathNodeType.Element:
                    break;
                default:
                    throw new InvalidOperationException(Res.GetString(Res.Xpn_BadPosition));
            }
            return CreateReader(); 
        }

        public virtual void WriteSubtree(XmlWriter writer) {
            if (null == writer)
                throw new ArgumentNullException("writer");
            writer.WriteNode(this, true);
        }

        public virtual object UnderlyingObject {
            get { return null; }
        }

        public virtual bool HasAttributes {
            get {
                if (!MoveToFirstAttribute())
                    return false;

                MoveToParent();
                return true;
            }
        }

        public virtual string GetAttribute(string localName, string namespaceURI) {
            string value;

            if (!MoveToAttribute(localName, namespaceURI))
                return "";

            value = Value;
            MoveToParent();

            return value;
        }

        public virtual bool MoveToAttribute(string localName, string namespaceURI) {
            if (MoveToFirstAttribute()) {
                do {
                    if (localName == LocalName && namespaceURI == NamespaceURI)
                        return true;
                }
                while (MoveToNextAttribute());

                MoveToParent();
            }

            return false;
        }

        public abstract bool MoveToFirstAttribute();

        public abstract bool MoveToNextAttribute();

        public virtual string GetNamespace(string name) {
            string value;

            if (!MoveToNamespace(name)) {
                if (name == "xml")
                    return XmlReservedNs.NsXml;
                if (name == "xmlns")
                    return XmlReservedNs.NsXmlNs;
                return string.Empty;
            }

            value = Value;
            MoveToParent();

            return value;
        }

        public virtual bool MoveToNamespace(string name) {
            if (MoveToFirstNamespace(XPathNamespaceScope.All)) {

                do {
                    if (name == LocalName)
                        return true;
                }
                while (MoveToNextNamespace(XPathNamespaceScope.All));

                MoveToParent();
            }

            return false;
        }

        public abstract bool MoveToFirstNamespace(XPathNamespaceScope namespaceScope);

        public abstract bool MoveToNextNamespace(XPathNamespaceScope namespaceScope);

        public bool MoveToFirstNamespace() { return MoveToFirstNamespace(XPathNamespaceScope.All); }

        public bool MoveToNextNamespace() { return MoveToNextNamespace(XPathNamespaceScope.All); }

        public abstract bool MoveToNext();

        public abstract bool MoveToPrevious();

        public virtual bool MoveToFirst() {
            switch (NodeType) {
                case XPathNodeType.Attribute:
                case XPathNodeType.Namespace:
                    // MoveToFirst should only succeed for content-typed nodes
                    return false;
            }

            if (!MoveToParent())
                return false;

            return MoveToFirstChild();
        }

        public abstract bool MoveToFirstChild();

        public abstract bool MoveToParent();

        public virtual void MoveToRoot() {
            while (MoveToParent())
                ;
        }

        public abstract bool MoveTo(XPathNavigator other);

        public abstract bool MoveToId(string id);

        public virtual bool MoveToChild(string localName, string namespaceURI) {
            if (MoveToFirstChild()) {
                do {
                    if (NodeType == XPathNodeType.Element && localName == LocalName && namespaceURI == NamespaceURI)
                        return true;
                }
                while (MoveToNext());
                MoveToParent();
            }

            return false;
        }

        public virtual bool MoveToChild(XPathNodeType type) {
            if (MoveToFirstChild()) {
                int mask = GetContentKindMask(type);
                do {
                    if (((1 << (int) NodeType) & mask) != 0)
                        return true;
                }
                while (MoveToNext());

                MoveToParent();
            }

            return false;
        }

        public virtual bool MoveToFollowing(string localName, string namespaceURI) {
            return MoveToFollowing(localName, namespaceURI, null);
        }

        public virtual bool MoveToFollowing(string localName, string namespaceURI, XPathNavigator end) {
            XPathNavigator navSave = Clone();

            if (end != null) {
                switch (end.NodeType) {
                    case XPathNodeType.Attribute:
                    case XPathNodeType.Namespace:
                        // Scan until we come to the next content-typed node 
                        // after the attribute or namespace node
                        end = end.Clone();
                        end.MoveToNonDescendant();
                        break;
                }
            }
            switch (NodeType) {
                case XPathNodeType.Attribute:
                case XPathNodeType.Namespace:
                    if (!MoveToParent()) {
                        // Restore previous position and return false
                        // MoveTo(navSave);
                        return false;
                    }
                    break;
            }
            do {
                if (!MoveToFirstChild()) {
                    // Look for next sibling
                    while (true) {
                        if (MoveToNext())
                            break;

                        if (!MoveToParent()) {
                            // Restore previous position and return false
                            MoveTo(navSave);
                            return false;
                        }
                    }
                }

                // Have we reached the end of the scan?
                if (end != null && IsSamePosition(end)) {
                    // Restore previous position and return false
                    MoveTo(navSave);
                    return false;
                }
            }
            while (NodeType != XPathNodeType.Element 
                   || localName != LocalName 
                   || namespaceURI != NamespaceURI);

            return true;
        }

        public virtual bool MoveToFollowing(XPathNodeType type) {
            return MoveToFollowing(type, null);
        }

        public virtual bool MoveToFollowing(XPathNodeType type, XPathNavigator end) {
            XPathNavigator navSave = Clone();
            int mask = GetContentKindMask(type);

            if (end != null) {
                switch (end.NodeType) {
                    case XPathNodeType.Attribute:
                    case XPathNodeType.Namespace:
                        // Scan until we come to the next content-typed node 
                        // after the attribute or namespace node
                        end = end.Clone();
                        end.MoveToNonDescendant();
                        break;
                }
            }
            switch (NodeType) {
                case XPathNodeType.Attribute:
                case XPathNodeType.Namespace:
                    if (!MoveToParent()) {
                        // Restore previous position and return false
                        // MoveTo(navSave);
                        return false;
                    }
                    break;
            }
            do {
                if (!MoveToFirstChild()) {
                    // Look for next sibling
                    while (true) {
                        if (MoveToNext())
                            break;

                        if (!MoveToParent()) {
                            // Restore previous position and return false
                            MoveTo(navSave);
                            return false;
                        }
                    }
                }

                // Have we reached the end of the scan?
                if (end != null && IsSamePosition(end)) {
                    // Restore previous position and return false
                    MoveTo(navSave);
                    return false;
                }
            }
            while (((1 << (int) NodeType) & mask) == 0);

            return true;
        }

        public virtual bool MoveToNext(string localName, string namespaceURI) {
            XPathNavigator navClone = Clone();

            while (MoveToNext()) {
                if (NodeType == XPathNodeType.Element && localName == LocalName && namespaceURI == NamespaceURI)
                    return true;
            }
            MoveTo(navClone);
            return false;
        }

        public virtual bool MoveToNext(XPathNodeType type) {
            XPathNavigator navClone = Clone();
            int mask = GetContentKindMask(type);

            while (MoveToNext()) {
                if (((1 << (int) NodeType) & mask) != 0)
                    return true;
            }

            MoveTo(navClone);
            return false;
        }

        public virtual bool HasChildren {
            get {
                if (MoveToFirstChild()) {
                    MoveToParent();
                    return true;
                }
                return false;
            }
        }

        public abstract bool IsSamePosition(XPathNavigator other);

        public virtual bool IsDescendant(XPathNavigator nav) {
            if (nav != null){
                nav = nav.Clone();
                while ( nav.MoveToParent() )
                    if (nav.IsSamePosition(this))
                        return true;
            }
            return false;
        }

        public virtual XmlNodeOrder ComparePosition( XPathNavigator nav ) {
            if (nav == null) {
                return XmlNodeOrder.Unknown;
            }

            if( IsSamePosition( nav ) )
                return XmlNodeOrder.Same;

            XPathNavigator n1 = this.Clone();
            XPathNavigator n2 = nav.Clone();

            int depth1 = GetDepth( n1.Clone() );
            int depth2 = GetDepth( n2.Clone() );

            if( depth1 > depth2 ) {
                while( depth1 > depth2 ) {
                    n1.MoveToParent();
                    depth1--;
                }
                if( n1.IsSamePosition(n2) )
                    return XmlNodeOrder.After;
            }

            if( depth2 > depth1 ) {
                while( depth2 > depth1 ) {
                    n2.MoveToParent();
                    depth2 --;
                }
                if( n1.IsSamePosition(n2) )
                    return XmlNodeOrder.Before;
            }

            XPathNavigator parent1 = n1.Clone();
            XPathNavigator parent2 = n2.Clone();

            while( true ) {
                if( !parent1.MoveToParent() || !parent2.MoveToParent() )
                    return XmlNodeOrder.Unknown;

                if( parent1.IsSamePosition( parent2 ) ) {
                    if (n1.GetType().ToString() != "Microsoft.VisualStudio.Modeling.StoreNavigator") {
                        Debug.Assert( CompareSiblings(n1.Clone(), n2.Clone()) != CompareSiblings(n2.Clone(), n1.Clone()), "IsSamePosition() on custom navigator returns incosistent results" );
                    }
                    return CompareSiblings(n1, n2);
                }

                n1.MoveToParent();
                n2.MoveToParent();
            }
        }

        public virtual IXmlSchemaInfo SchemaInfo {
            get { return this as IXmlSchemaInfo; }
        }

        public virtual bool CheckValidity(XmlSchemaSet schemas, ValidationEventHandler validationEventHandler) {
            IXmlSchemaInfo schemaInfo;
            XmlSchemaType schemaType = null;
            XmlSchemaElement schemaElement = null;
            XmlSchemaAttribute schemaAttribute = null;

            switch (NodeType) {
                case XPathNodeType.Root:
                    if (schemas == null) {
                        throw new InvalidOperationException(Res.GetString(Res.XPathDocument_MissingSchemas));
                    }
                    schemaType = null;
                    break;
                case XPathNodeType.Element:
                    if (schemas == null) {
                        throw new InvalidOperationException(Res.GetString(Res.XPathDocument_MissingSchemas)); 
                    }
                    schemaInfo = SchemaInfo;
                    if (schemaInfo != null) {
                        schemaType = schemaInfo.SchemaType;
                        schemaElement = schemaInfo.SchemaElement;
                    }
                    if (schemaType == null
                        && schemaElement == null) {
                        throw new InvalidOperationException(Res.GetString(Res.XPathDocument_NotEnoughSchemaInfo, null));
                    }
                    break;
                case XPathNodeType.Attribute:
                    if (schemas == null) {
                        throw new InvalidOperationException(Res.GetString(Res.XPathDocument_MissingSchemas)); 
                    }
                    schemaInfo = SchemaInfo;
                    if (schemaInfo != null) {
                        schemaType = schemaInfo.SchemaType;
                        schemaAttribute = schemaInfo.SchemaAttribute;
                    }
                    if (schemaType == null
                        && schemaAttribute == null) {
                        throw new InvalidOperationException(Res.GetString(Res.XPathDocument_NotEnoughSchemaInfo, null));
                    }
                    break;
                default:
                    throw new InvalidOperationException(Res.GetString(Res.XPathDocument_ValidateInvalidNodeType, null));

            }
           
            Debug.Assert( schemaType != null  || this.NodeType == XPathNodeType.Root, "schemaType != null  || this.NodeType == XPathNodeType.Root" );

            XmlReader reader = CreateReader();

            CheckValidityHelper validityTracker = new CheckValidityHelper( validationEventHandler, reader as XPathNavigatorReader );
            validationEventHandler = new ValidationEventHandler( validityTracker.ValidationCallback );
            XmlReader validatingReader = GetValidatingReader( reader, schemas, validationEventHandler, schemaType, schemaElement, schemaAttribute );

            while( validatingReader.Read() )
                ;

            return validityTracker.IsValid;
        }

        private XmlReader GetValidatingReader( XmlReader reader, XmlSchemaSet schemas, ValidationEventHandler validationEvent, XmlSchemaType schemaType, XmlSchemaElement schemaElement, XmlSchemaAttribute schemaAttribute ) {
            if (schemaAttribute != null) {
                return schemaAttribute.Validate(reader, null, schemas, validationEvent);
            }
            else if (schemaElement != null) {
                return schemaElement.Validate(reader, null, schemas, validationEvent);
            }
            else if (schemaType != null) {
                return schemaType.Validate(reader, null, schemas, validationEvent);
            }
            Debug.Assert( schemas != null, "schemas != null" );
            XmlReaderSettings readerSettings = new XmlReaderSettings();
            readerSettings.ConformanceLevel = ConformanceLevel.Auto;
            readerSettings.ValidationType = ValidationType.Schema;
            readerSettings.Schemas = schemas;
            readerSettings.ValidationEventHandler += validationEvent;
            return XmlReader.Create( reader, readerSettings );
        }

        class CheckValidityHelper {
            bool isValid;
            ValidationEventHandler nextEventHandler;
            XPathNavigatorReader reader;
            
            internal CheckValidityHelper( ValidationEventHandler nextEventHandler, XPathNavigatorReader reader ) {
                this.isValid = true;
                this.nextEventHandler = nextEventHandler;
                this.reader = reader;
            }

            internal void ValidationCallback( object sender, ValidationEventArgs args ) {
                Debug.Assert( args != null );
                if ( args.Severity == XmlSeverityType.Error )
                    this.isValid = false;
                XmlSchemaValidationException exception = args.Exception as XmlSchemaValidationException;
                if (exception != null && reader != null)
                    exception.SetSourceObject(reader.UnderlyingObject);

                if (this.nextEventHandler != null) {
                    this.nextEventHandler( sender, args );
                }
                else if (exception != null && args.Severity == XmlSeverityType.Error) {
                    throw exception;
                }
            }

            internal bool IsValid {
                get { return this.isValid; }
            }
        }

        public virtual XPathExpression Compile(string xpath) {
            return XPathExpression.Compile(xpath);
        }

        public virtual XPathNavigator SelectSingleNode(string xpath) {
            return SelectSingleNode(XPathExpression.Compile(xpath));
        }

        public virtual XPathNavigator SelectSingleNode(string xpath, IXmlNamespaceResolver resolver) {
            return SelectSingleNode(XPathExpression.Compile(xpath, resolver));
        }

        public virtual XPathNavigator SelectSingleNode(XPathExpression expression) {
            // 
            XPathNodeIterator iter = this.Select(expression);
            if (iter.MoveNext()) {
                return iter.Current;
            }
            return null;
        }

        public virtual XPathNodeIterator Select(string xpath) {
            Contract.Ensures(Contract.Result<XPathNodeIterator>() != null);

            return this.Select(XPathExpression.Compile(xpath));
        }

        public virtual XPathNodeIterator Select(string xpath, IXmlNamespaceResolver resolver) {
            Contract.Ensures(Contract.Result<XPathNodeIterator>() != null);

            return this.Select(XPathExpression.Compile(xpath, resolver));
        }

        public virtual XPathNodeIterator Select(XPathExpression expr) {
            Contract.Ensures(Contract.Result<XPathNodeIterator>() != null);

            XPathNodeIterator result = Evaluate(expr) as XPathNodeIterator;
            if (result == null) {
                throw XPathException.Create(Res.Xp_NodeSetExpected);
            }
            return result;
        }

        public virtual object Evaluate(string xpath) {
            return Evaluate(XPathExpression.Compile(xpath), null);
        }

        public virtual object Evaluate(string xpath, IXmlNamespaceResolver resolver) {
            return this.Evaluate(XPathExpression.Compile(xpath, resolver));
        }

        public virtual object Evaluate(XPathExpression expr) {
            return Evaluate(expr, null);
        }

        public virtual object Evaluate(XPathExpression expr, XPathNodeIterator context) {
            CompiledXpathExpr cexpr = expr as CompiledXpathExpr;
            if (cexpr == null) {
                throw XPathException.Create(Res.Xp_BadQueryObject);
            }
            Query query = Query.Clone(cexpr.QueryTree);
            query.Reset();

            if (context == null) {
                context = new XPathSingletonIterator(this.Clone(), /*moved:*/true);
            }

            object result = query.Evaluate(context);

            if (result is XPathNodeIterator) {
                return new XPathSelectionIterator(context.Current, query);
            }

            return result;
        }

        public virtual bool Matches( XPathExpression expr ) {
            CompiledXpathExpr cexpr = expr as CompiledXpathExpr;
            if( cexpr == null )
                throw XPathException.Create(Res.Xp_BadQueryObject);

            // We should clone query because some Query.MatchNode() alter expression state and this may brake
            // SelectionIterators that are runing using this Query
            // Excample of MatchNode() that alret the state is FilterQuery.MatchNode()
            Query query = Query.Clone(cexpr.QueryTree);  

            try {
                return query.MatchNode(this) != null;
            }
            catch(XPathException) {
                throw XPathException.Create(Res.Xp_InvalidPattern, cexpr.Expression);
            }
        }

        public virtual bool Matches(string xpath) {
            return Matches(CompileMatchPattern(xpath));
        }

        public virtual XPathNodeIterator SelectChildren( XPathNodeType type ) {
            return new XPathChildIterator( this.Clone(), type );
        }

        public virtual XPathNodeIterator SelectChildren( string name, string namespaceURI ) {
            return new XPathChildIterator( this.Clone(), name, namespaceURI );
        }

        public virtual XPathNodeIterator SelectAncestors( XPathNodeType type, bool matchSelf ) {
            return new XPathAncestorIterator( this.Clone(), type, matchSelf );
        }

        public virtual XPathNodeIterator SelectAncestors( string name, string namespaceURI, bool matchSelf ) {
            return new XPathAncestorIterator( this.Clone(), name, namespaceURI, matchSelf );
        }

        public virtual XPathNodeIterator SelectDescendants( XPathNodeType type, bool matchSelf ) {
            return new XPathDescendantIterator( this.Clone(), type, matchSelf );
        }

        public virtual XPathNodeIterator SelectDescendants( string name, string namespaceURI, bool matchSelf ) {
            return new XPathDescendantIterator( this.Clone(), name, namespaceURI, matchSelf );
        }

        public virtual bool CanEdit {
            get {
                return false;
            }
        }

        public virtual XmlWriter PrependChild() {
            throw new NotSupportedException();
        }

        public virtual XmlWriter AppendChild() {
            throw new NotSupportedException();
        }

        public virtual XmlWriter InsertAfter() {
            throw new NotSupportedException();
        }

        public virtual XmlWriter InsertBefore() {
            throw new NotSupportedException();
        }

        public virtual XmlWriter CreateAttributes() {
            throw new NotSupportedException();
        }

        public virtual XmlWriter ReplaceRange(XPathNavigator lastSiblingToReplace) {
            throw new NotSupportedException();
        }

        public virtual void ReplaceSelf(string newNode) {
            XmlReader reader = CreateContextReader(newNode, false);
            ReplaceSelf(reader);
        }

        public virtual void ReplaceSelf(XmlReader newNode) {
            if (newNode == null) {
                throw new ArgumentNullException("newNode");
            }
            XPathNodeType type = NodeType;
            if (type == XPathNodeType.Root
                || type == XPathNodeType.Attribute
                || type == XPathNodeType.Namespace) {
                throw new InvalidOperationException(Res.GetString(Res.Xpn_BadPosition));
            }
            XmlWriter writer = ReplaceRange(this);
            BuildSubtree(newNode, writer);
            writer.Close();
        }

        public virtual void ReplaceSelf(XPathNavigator newNode) {
            if (newNode == null) {
                throw new ArgumentNullException("newNode");
            }
            XmlReader reader = newNode.CreateReader();
            ReplaceSelf(reader);
        }

        // Returns the markup representing the current node and all of its children.
        public virtual string OuterXml {
            get {
                StringWriter stringWriter;
                XmlWriterSettings writerSettings;
                XmlWriter xmlWriter;

                // Attributes and namespaces are not allowed at the top-level by the well-formed writer
                if (NodeType == XPathNodeType.Attribute) {
                    return string.Concat(Name, "=\"", Value, "\"");
                }
                else if (NodeType == XPathNodeType.Namespace) {
                    if (LocalName.Length == 0)
                        return string.Concat("xmlns=\"", Value, "\"");
                    else
                        return string.Concat("xmlns:", LocalName, "=\"", Value, "\"");
                }

                stringWriter = new StringWriter(CultureInfo.InvariantCulture);

                writerSettings = new XmlWriterSettings();
                writerSettings.Indent = true;
                writerSettings.OmitXmlDeclaration = true;
                writerSettings.ConformanceLevel = ConformanceLevel.Auto;

                xmlWriter = XmlWriter.Create(stringWriter, writerSettings);
                try {
                    xmlWriter.WriteNode(this, true);
                }
                finally {
                    xmlWriter.Close();
                }

                return stringWriter.ToString();
            }

            set {
                ReplaceSelf(value);
            }
        }

        // Returns the markup representing just the children of the current node.
        public virtual string InnerXml {
            get {
                switch (NodeType) {
                    case XPathNodeType.Root:
                    case XPathNodeType.Element:
                        StringWriter stringWriter;
                        XmlWriterSettings writerSettings;
                        XmlWriter xmlWriter;

                        stringWriter = new StringWriter(CultureInfo.InvariantCulture);

                        writerSettings = new XmlWriterSettings();
                        writerSettings.Indent = true;
                        writerSettings.OmitXmlDeclaration = true;
                        writerSettings.ConformanceLevel = ConformanceLevel.Auto;
                        xmlWriter = XmlWriter.Create(stringWriter, writerSettings);

                        try {
                            if (MoveToFirstChild()) {
                                do {
                                    xmlWriter.WriteNode(this, true);
                                }
                                while (MoveToNext());

                                // Restore position
                                MoveToParent();
                            }
                        }
                        finally {
                            xmlWriter.Close();
                        }
                        return stringWriter.ToString();
                    case XPathNodeType.Attribute:
                    case XPathNodeType.Namespace:
                        return Value;
                    default:
                        return string.Empty;
                }
            }

            set {
                if (value == null) {
                    throw new ArgumentNullException("value");
                }

                switch (NodeType) {
                    case XPathNodeType.Root:
                    case XPathNodeType.Element:
                        XPathNavigator edit = CreateNavigator();
                        while (edit.MoveToFirstChild()) {
                            edit.DeleteSelf();
                        }
                        if (value.Length != 0) {
                            edit.AppendChild(value);
                        }
                        break;
                    case XPathNodeType.Attribute:
                        SetValue(value);
                        break;
                    default:
                        throw new InvalidOperationException(Res.GetString(Res.Xpn_BadPosition));
                }
            }
        }

        public virtual void AppendChild(string newChild) {
            XmlReader reader = CreateContextReader(newChild, true);
            AppendChild(reader);
        }

        public virtual void AppendChild(XmlReader newChild) {
            if (newChild == null) {
                throw new ArgumentNullException("newChild");
            }
            XmlWriter writer = AppendChild();
            BuildSubtree(newChild, writer);
            writer.Close();
        }

        public virtual void AppendChild(XPathNavigator newChild) {
            if (newChild == null) {
                throw new ArgumentNullException("newChild");
            }
            if (!IsValidChildType(newChild.NodeType)) {
                throw new InvalidOperationException(Res.GetString(Res.Xpn_BadPosition));
            }
            XmlReader reader = newChild.CreateReader();
            AppendChild(reader);
        }

        public virtual void PrependChild(string newChild) {
            XmlReader reader = CreateContextReader(newChild, true);
            PrependChild(reader);
        }

        public virtual void PrependChild(XmlReader newChild) {
            if (newChild == null) {
                throw new ArgumentNullException("newChild");
            }
            XmlWriter writer = PrependChild();
            BuildSubtree(newChild, writer);
            writer.Close();
        }

        public virtual void PrependChild(XPathNavigator newChild) {
            if (newChild == null) {
                throw new ArgumentNullException("newChild");
            }
            if (!IsValidChildType(newChild.NodeType)) {
                throw new InvalidOperationException(Res.GetString(Res.Xpn_BadPosition));
            }
            XmlReader reader = newChild.CreateReader();
            PrependChild(reader);
        }

        public virtual void InsertBefore(string newSibling) {
            XmlReader reader = CreateContextReader(newSibling, false);
            InsertBefore(reader);
        }

        public virtual void InsertBefore(XmlReader newSibling) {
            if (newSibling == null) {
                throw new ArgumentNullException("newSibling");
            }
            XmlWriter writer = InsertBefore();
            BuildSubtree(newSibling, writer);
            writer.Close();
        }

        public virtual void InsertBefore(XPathNavigator newSibling) {
            if (newSibling == null) {
                throw new ArgumentNullException("newSibling");
            }
            if (!IsValidSiblingType(newSibling.NodeType)) {
                throw new InvalidOperationException(Res.GetString(Res.Xpn_BadPosition));
            }
            XmlReader reader = newSibling.CreateReader();
            InsertBefore(reader);
        }

        public virtual void InsertAfter(string newSibling) {
            XmlReader reader = CreateContextReader(newSibling, false);
            InsertAfter(reader);
        }

        public virtual void InsertAfter(XmlReader newSibling) {
            if (newSibling == null) {
                throw new ArgumentNullException("newSibling");
            }
            XmlWriter writer = InsertAfter();
            BuildSubtree(newSibling, writer);
            writer.Close();
        }

        public virtual void InsertAfter(XPathNavigator newSibling) {
            if (newSibling == null) {
                throw new ArgumentNullException("newSibling");
            }
            if (!IsValidSiblingType(newSibling.NodeType)) {
                throw new InvalidOperationException(Res.GetString(Res.Xpn_BadPosition));
            }
            XmlReader reader = newSibling.CreateReader();
            InsertAfter(reader);
        }

        public virtual void DeleteRange(XPathNavigator lastSiblingToDelete) {
            throw new NotSupportedException();
        }

        public virtual void DeleteSelf() {
            DeleteRange(this);
        }

        public virtual void PrependChildElement(string prefix, string localName, string namespaceURI, string value) {
            XmlWriter writer = PrependChild();
            writer.WriteStartElement(prefix, localName, namespaceURI);
            if (value != null) {
                writer.WriteString(value);
            }
            writer.WriteEndElement();
            writer.Close();
        }

        public virtual void AppendChildElement(string prefix, string localName, string namespaceURI, string value) {
            XmlWriter writer = AppendChild();
            writer.WriteStartElement(prefix, localName, namespaceURI);
            if (value != null) {
                writer.WriteString(value);
            }
            writer.WriteEndElement();
            writer.Close();
        }

        public virtual void InsertElementBefore(string prefix, string localName, string namespaceURI, string value) {
            XmlWriter writer = InsertBefore();
            writer.WriteStartElement(prefix, localName, namespaceURI);
            if (value != null) {
                writer.WriteString(value);
            }
            writer.WriteEndElement();
            writer.Close();
        }

        public virtual void InsertElementAfter(string prefix, string localName, string namespaceURI, string value) {
            XmlWriter writer = InsertAfter();
            writer.WriteStartElement(prefix, localName, namespaceURI);
            if (value != null) {
                writer.WriteString(value);
            }
            writer.WriteEndElement();
            writer.Close();
        }

        public virtual void CreateAttribute(string prefix, string localName, string namespaceURI, string value) {
            XmlWriter writer = CreateAttributes();
            writer.WriteStartAttribute(prefix, localName, namespaceURI);
            if (value != null) {
                writer.WriteString(value);
            }
            writer.WriteEndAttribute();
            writer.Close();
        }

        //-----------------------------------------------
        // Internal
        //-----------------------------------------------

        internal bool MoveToPrevious(string localName, string namespaceURI) {
            XPathNavigator navClone = Clone();

            localName = (localName != null) ? NameTable.Get(localName) : null;
            while (MoveToPrevious()) {
                if (NodeType == XPathNodeType.Element && (object) localName == (object) LocalName && namespaceURI == NamespaceURI)
                    return true;
            }

            MoveTo(navClone);
            return false;
        }

        internal bool MoveToPrevious(XPathNodeType type) {
            XPathNavigator navClone = Clone();
            int mask = GetContentKindMask(type);

            while (MoveToPrevious()) {
                if (((1 << (int) NodeType) & mask) != 0)
                    return true;
            }

            MoveTo(navClone);
            return false;
        }

        internal bool MoveToNonDescendant() {
            // If current node is document, there is no next non-descendant
            if (NodeType == XPathNodeType.Root)
                return false;

            // If sibling exists, it is the next non-descendant
            if (MoveToNext())
                return true;

            // The current node is either an attribute, namespace, or last child node
            XPathNavigator navSave = Clone();

            if (!MoveToParent())
                return false;

            switch (navSave.NodeType) {
                case XPathNodeType.Attribute:
                case XPathNodeType.Namespace:
                    // Next node in document order is first content-child of parent
                    if (MoveToFirstChild())
                        return true;
                    break;
            }

            while (!MoveToNext()) {
                if (!MoveToParent()) {
                    // Restore original position and return false
                    MoveTo(navSave);
                    return false;
                }
            }

            return true;
        }

        /// <summary>
        /// Returns ordinal number of attribute, namespace or child node within its parent.
        /// Order is reversed for attributes and child nodes to avoid O(N**2) running time.
        /// This property is useful for debugging, and also used in UniqueId implementation.
        /// </summary>
        internal uint IndexInParent {
            get {
                XPathNavigator nav = this.Clone();
                uint idx = 0;

                switch (NodeType) {
                    case XPathNodeType.Attribute:
                        while (nav.MoveToNextAttribute()) {
                            idx ++;
                        }
                        break;
                    case XPathNodeType.Namespace:
                        while (nav.MoveToNextNamespace()) {
                            idx ++;
                        }
                        break;
                    default:
                        while (nav.MoveToNext()) {
                            idx ++;
                        }
                        break;
                }
                return idx;
            }
        }

        internal static readonly char[] NodeTypeLetter = new char[] {
            'R',    // Root
            'E',    // Element
            'A',    // Attribute
            'N',    // Namespace
            'T',    // Text
            'S',    // SignificantWhitespace
            'W',    // Whitespace
            'P',    // ProcessingInstruction
            'C',    // Comment
            'X',    // All
        };

        internal static readonly char[] UniqueIdTbl = new char[] {
            'A',  'B',  'C',  'D',  'E',  'F',  'G',  'H',  'I',  'J',
            'K',  'L',  'M',  'N',  'O',  'P',  'Q',  'R',  'S',  'T',
            'U',  'V',  'W',  'X',  'Y',  'Z',  '1',  '2',  '3',  '4',
            '5',  '6'
        };

        // Requirements for id:
        //  1. must consist of alphanumeric characters only
        //  2. must begin with an alphabetic character
        //  3. same id is generated for the same node
        //  4. ids are unique
        //
        //  id = node type letter + reverse path to root in terms of encoded IndexInParent integers from node to root seperated by 0's if needed
        internal virtual string UniqueId {
            get {
                XPathNavigator  nav = this.Clone();
                StringBuilder sb = new StringBuilder();

                // Ensure distinguishing attributes, namespaces and child nodes
                sb.Append(NodeTypeLetter[(int)NodeType]);

                while (true) {
                    uint idx = nav.IndexInParent;
                    if (!nav.MoveToParent()) {
                        break;
                    }
                    if (idx <= 0x1f) {
                        sb.Append(UniqueIdTbl[idx]);
                    } else {
                        sb.Append('0');
                        do {
                            sb.Append(UniqueIdTbl[idx & 0x1f]);
                            idx >>= 5;
                        } while (idx != 0);
                        sb.Append('0');
                    }
                }
                return sb.ToString();
            }
        }

        private static XPathExpression CompileMatchPattern(string xpath) {
            bool hasPrefix;
            Query query = new QueryBuilder().BuildPatternQuery(xpath, out hasPrefix);
            return new CompiledXpathExpr(query, xpath, hasPrefix);
        }

        private static int GetDepth(XPathNavigator nav) {
            int depth = 0;
            while (nav.MoveToParent()) {
                depth++;
            }
            return depth;
        }

        // XPath based comparison for namespaces, attributes and other 
        // items with the same parent element.
        //
        //                 n2
        //                 namespace(0)    attribute(-1)   other(-2)
        // n1
        // namespace(0)    ?(0)            before(-1)      before(-2)
        // attribute(1)    after(1)        ?(0)            before(-1)
        // other    (2)    after(2)        after(1)        ?(0)
        private XmlNodeOrder CompareSiblings(XPathNavigator n1, XPathNavigator n2) {
            int cmp = 0;

#if DEBUG
            Debug.Assert(!n1.IsSamePosition(n2));
            XPathNavigator p1 = n1.Clone(), p2 = n2.Clone();
            Debug.Assert(p1.MoveToParent() && p2.MoveToParent() && p1.IsSamePosition(p2));
#endif
            switch (n1.NodeType) {
                case XPathNodeType.Namespace: 
                    break;
                case XPathNodeType.Attribute: 
                    cmp += 1; 
                    break;
                default:
                    cmp += 2; 
                    break;
            }
            switch (n2.NodeType) {
                case XPathNodeType.Namespace: 
                    if (cmp == 0) {
                        while (n1.MoveToNextNamespace()) {
                            if (n1.IsSamePosition(n2)) {
                                return XmlNodeOrder.Before;
                            }
                        }
                    }
                    break; 
                case XPathNodeType.Attribute: 
                    cmp -= 1; 
                    if (cmp == 0) {
                        while (n1.MoveToNextAttribute()) {
                            if (n1.IsSamePosition(n2)) {
                                return XmlNodeOrder.Before;
                            }
                        }
                    }
                    break;
                default:
                    cmp -= 2; 
                    if (cmp == 0) {
                        while (n1.MoveToNext()) {
                            if (n1.IsSamePosition(n2)) {
                                return XmlNodeOrder.Before;
                            }
                        }
                    }
                    break;
            }
            return cmp < 0 ? XmlNodeOrder.Before : XmlNodeOrder.After;
        }

        internal static XmlNamespaceManager GetNamespaces( IXmlNamespaceResolver resolver ) {
            XmlNamespaceManager mngr = new XmlNamespaceManager(new NameTable());
            IDictionary<string,string> dictionary = resolver.GetNamespacesInScope( XmlNamespaceScope.All );
            foreach ( KeyValuePair<string,string> pair in dictionary ) {
                //"xmlns " is always in the namespace manager so adding it would throw an exception
                if( pair.Key != "xmlns" )
                    mngr.AddNamespace( pair.Key, pair.Value );
            }
            return mngr;
        }

        // Get mask that will allow XPathNodeType content matching to be performed using only a shift and an and operation
        internal const int AllMask = 0x7FFFFFFF;
        internal const int NoAttrNmspMask = AllMask & ~(1 << (int) XPathNodeType.Attribute) & ~(1 << (int) XPathNodeType.Namespace);
        internal const int TextMask = (1 << (int) XPathNodeType.Text) | (1 << (int) XPathNodeType.SignificantWhitespace) | (1 << (int) XPathNodeType.Whitespace);
        internal static readonly int[] ContentKindMasks = {
            (1 << (int) XPathNodeType.Root),                        // Root
            (1 << (int) XPathNodeType.Element),                     // Element
            0,                                                      // Attribute (not content)
            0,                                                      // Namespace (not content)
            TextMask,                                               // Text
            (1 << (int) XPathNodeType.SignificantWhitespace),       // SignificantWhitespace
            (1 << (int) XPathNodeType.Whitespace),                  // Whitespace
            (1 << (int) XPathNodeType.ProcessingInstruction),       // ProcessingInstruction
            (1 << (int) XPathNodeType.Comment),                     // Comment
            NoAttrNmspMask,                                         // All
        };

        internal static int GetContentKindMask(XPathNodeType type) {
            return ContentKindMasks[(int) type];
        }

        internal static int GetKindMask(XPathNodeType type) {
            if (type == XPathNodeType.All)
                return AllMask;
            else if (type == XPathNodeType.Text)
                return TextMask;

            return (1 << (int) type);
        }

        internal static bool IsText(XPathNodeType type) {
            //return ((1 << (int) type) & TextMask) != 0;
            return (uint)(type - XPathNodeType.Text) <= (XPathNodeType.Whitespace - XPathNodeType.Text);
        }

        // Lax check for potential child item.
        private bool IsValidChildType(XPathNodeType type) {
            switch (NodeType) {
                case XPathNodeType.Root:
                    switch (type) {
                        case XPathNodeType.Element:
                        case XPathNodeType.SignificantWhitespace:
                        case XPathNodeType.Whitespace:
                        case XPathNodeType.ProcessingInstruction:
                        case XPathNodeType.Comment:
                            return true;
                    }
                    break;
                case XPathNodeType.Element:
                    switch (type) {
                        case XPathNodeType.Element:
                        case XPathNodeType.Text:
                        case XPathNodeType.SignificantWhitespace:
                        case XPathNodeType.Whitespace:
                        case XPathNodeType.ProcessingInstruction:
                        case XPathNodeType.Comment:
                            return true;
                    }
                    break;
            }
            return false;
        }

        // Lax check for potential sibling item. 
        private bool IsValidSiblingType(XPathNodeType type) {
            switch (NodeType) {
                case XPathNodeType.Element:
                case XPathNodeType.Text:
                case XPathNodeType.SignificantWhitespace:
                case XPathNodeType.Whitespace:
                case XPathNodeType.ProcessingInstruction:
                case XPathNodeType.Comment:
                    switch (type) {
                        case XPathNodeType.Element:
                        case XPathNodeType.Text:
                        case XPathNodeType.SignificantWhitespace:
                        case XPathNodeType.Whitespace:
                        case XPathNodeType.ProcessingInstruction:
                        case XPathNodeType.Comment:
                            return true;
                    }
                    break;
            }
            return false;
        }

        private XmlReader CreateReader() {
            return XPathNavigatorReader.Create(this);
        }

        private XmlReader CreateContextReader(string xml, bool fromCurrentNode) {
            if (xml == null) {
                throw new ArgumentNullException("xml");
            }

            // We have to set the namespace context for the reader.
            XPathNavigator editor = CreateNavigator();
            // scope starts from parent.
            XmlNamespaceManager mgr = new XmlNamespaceManager( NameTable );
            if (!fromCurrentNode) {
                editor.MoveToParent(); // should always succeed.
            }
            if (editor.MoveToFirstNamespace(XPathNamespaceScope.All)) {
                do {
                    mgr.AddNamespace(editor.LocalName, editor.Value);
                } 
                while (editor.MoveToNextNamespace(XPathNamespaceScope.All));
            }
            // 
            XmlParserContext context = new XmlParserContext(NameTable, mgr, null, XmlSpace.Default);
            XmlTextReader reader = new XmlTextReader(xml, XmlNodeType.Element, context);
            // 
            reader.WhitespaceHandling = WhitespaceHandling.Significant;
            return reader;
        }

        internal void BuildSubtree(XmlReader reader, XmlWriter writer) {
            // important (perf) string literal...
            string xmlnsUri = XmlReservedNs.NsXmlNs; // http://www.w3.org/2000/xmlns/
            ReadState readState = reader.ReadState;

            if (readState != ReadState.Initial
                && readState != ReadState.Interactive) {
                throw new ArgumentException(Res.GetString(Res.Xml_InvalidOperation), "reader");
            }
            int level = 0;
            if ( readState == ReadState.Initial ) {
                if( !reader.Read() )
                    return;
                level++; // if start in initial, read everything (not just first)
            }
            do {
                switch (reader.NodeType) {
                    case XmlNodeType.Element:
                        writer.WriteStartElement( reader.Prefix,  reader.LocalName, reader.NamespaceURI );
                        bool isEmptyElement = reader.IsEmptyElement;

                        while (reader.MoveToNextAttribute()) {                                
                            if ((object) reader.NamespaceURI == (object) xmlnsUri) {
                                if (reader.Prefix.Length == 0) {
                                    // Default namespace declaration "xmlns"
                                    Debug.Assert(reader.LocalName == "xmlns");
                                    writer.WriteAttributeString( "", "xmlns", xmlnsUri, reader.Value );
                                }
                                else {
                                    Debug.Assert(reader.Prefix == "xmlns");
                                    writer.WriteAttributeString( "xmlns", reader.LocalName, xmlnsUri, reader.Value );
                                }
                            }
                            else {
                                writer.WriteStartAttribute(reader.Prefix, reader.LocalName, reader.NamespaceURI);
                                writer.WriteString(reader.Value);
                                writer.WriteEndAttribute();
                            }
                        }

                        reader.MoveToElement();
                        if (isEmptyElement) {
                            // there might still be a value, if there is a default value specified in the schema
                            writer.WriteEndElement();
                        }
                        else {
                            level++;
                        }
                        break;
                    case XmlNodeType.EndElement:
                        writer.WriteFullEndElement();
                        //should not read beyond the level of the reader's original position.
                        level--;
                        break;
                    case XmlNodeType.Text:
                    case XmlNodeType.CDATA:
                        writer.WriteString( reader.Value );
                        break;
                    case XmlNodeType.SignificantWhitespace:
                    case XmlNodeType.Whitespace:
                        // 
                        writer.WriteString( reader.Value );
                        break;
                    case XmlNodeType.Comment:
                        writer.WriteComment( reader.Value );
                        break;
                    case XmlNodeType.ProcessingInstruction:
                        writer.WriteProcessingInstruction( reader.LocalName , reader.Value);
                        break;
                    case XmlNodeType.EntityReference:
                        reader.ResolveEntity(); // 
                        break;
                    case XmlNodeType.EndEntity:
                    case XmlNodeType.None:
                    case XmlNodeType.DocumentType:
                    case XmlNodeType.XmlDeclaration:
                        break;                    
                    case XmlNodeType.Attribute:
                        if ((object) reader.NamespaceURI == (object) xmlnsUri) {
                            if (reader.Prefix.Length == 0) {
                                // Default namespace declaration "xmlns"
                                Debug.Assert(reader.LocalName == "xmlns");
                                writer.WriteAttributeString( "", "xmlns", xmlnsUri, reader.Value );
                            }
                            else {
                                Debug.Assert(reader.Prefix == "xmlns");
                                writer.WriteAttributeString( "xmlns", reader.LocalName, xmlnsUri, reader.Value );
                            }
                        }
                        else {
                            writer.WriteStartAttribute(reader.Prefix, reader.LocalName, reader.NamespaceURI);
                            writer.WriteString(reader.Value);
                            writer.WriteEndAttribute();
                        }
                        break;
                }
            } 
            while( reader.Read() && ( level > 0 ) );
        }

        private object debuggerDisplayProxy { get { return new DebuggerDisplayProxy(this); } }

        [DebuggerDisplay("{ToString()}")]
        internal struct DebuggerDisplayProxy {
            XPathNavigator nav;
            public DebuggerDisplayProxy(XPathNavigator nav) {
                this.nav = nav;
            }
            public override string ToString() {
                string result = nav.NodeType.ToString();
                switch (nav.NodeType) {
                case XPathNodeType.Element              :
                    result += ", Name=\"" + nav.Name + '"';
                    break;
                case XPathNodeType.Attribute:
                case XPathNodeType.Namespace            :
                case XPathNodeType.ProcessingInstruction:
                    result += ", Name=\"" + nav.Name + '"';
                    result += ", Value=\"" + XmlConvert.EscapeValueForDebuggerDisplay(nav.Value) + '"';
                    break;
                case XPathNodeType.Text                 :
                case XPathNodeType.Whitespace           :
                case XPathNodeType.SignificantWhitespace:
                case XPathNodeType.Comment              :
                    result += ", Value=\"" + XmlConvert.EscapeValueForDebuggerDisplay(nav.Value) + '"';
                    break;
                }
                return result;
            }
        }
    }

#if CONTRACTS_FULL
    [ContractClassFor(typeof(XPathNavigator))]
    internal abstract class XPathNavigatorContract : XPathNavigator
    {
        public override XPathNavigator Clone()
        {
            Contract.Ensures(Contract.Result<XPathNavigator>() != null);
            return default(XPathNavigator);
        }

        public override XmlNameTable NameTable { 
            get {
                Contract.Ensures(Contract.Result<XmlNameTable>() != null);
                return default(XmlNameTable);
            }
        }
    }
#endif
}