System.Xml.XPath.XPathNavigator.BuildSubtree C# (CSharp) Method

        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(SR.Xml_InvalidOperation, nameof(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));
        }