System.Runtime.Serialization.Json.XmlJsonWriter.WriteStartAttribute C# (CSharp) Method

        public override void WriteStartAttribute(string prefix, string localName, string ns)
        {
            if (IsClosed)
            {
                ThrowClosed();
            }
            if (!string.IsNullOrEmpty(prefix))
            {
                if (IsWritingNameWithMapping && prefix == JsonGlobals.xmlnsPrefix)
                {
                    if (ns != null && ns != xmlnsNamespace)
                    {
                        throw new ArgumentException(SR.Format(SR.XmlPrefixBoundToNamespace, "xmlns", xmlnsNamespace, ns), nameof(ns));
                    }
                }
                else
                {
                    throw new ArgumentException(SR.Format(SR.JsonPrefixMustBeNullOrEmpty, prefix), nameof(prefix));
                }
            }
            else
            {
                if (IsWritingNameWithMapping && ns == xmlnsNamespace && localName != JsonGlobals.xmlnsPrefix)
                {
                    prefix = JsonGlobals.xmlnsPrefix;
                }
            }
            if (!string.IsNullOrEmpty(ns))
            {
                if (IsWritingNameWithMapping && ns == xmlnsNamespace)
                {
                    prefix = JsonGlobals.xmlnsPrefix;
                }
                else if (string.IsNullOrEmpty(prefix) && localName == JsonGlobals.xmlnsPrefix && ns == xmlnsNamespace)
                {
                    prefix = JsonGlobals.xmlnsPrefix;
                    _isWritingXmlnsAttributeDefaultNs = true;
                }
                else
                {
                    throw new ArgumentException(SR.Format(SR.JsonNamespaceMustBeEmpty, ns), nameof(ns));
                }
            }
            if (localName == null)
            {
                throw new ArgumentNullException(nameof(localName));
            }
            if (localName.Length == 0)
            {
                throw new ArgumentException(SR.JsonInvalidLocalNameEmpty, nameof(localName));
            }
            if ((_nodeType != JsonNodeType.Element) && !_wroteServerTypeAttribute)
            {
                throw new XmlException(SR.JsonAttributeMustHaveElement);
            }
            if (HasOpenAttribute)
            {
                throw new XmlException(SR.Format(SR.JsonOpenAttributeMustBeClosedFirst, "WriteStartAttribute"));
            }
            if (prefix == JsonGlobals.xmlnsPrefix)
            {
                _isWritingXmlnsAttribute = true;
            }
            else if (localName == JsonGlobals.typeString)
            {
                if (_dataType != JsonDataType.None)
                {
                    throw new XmlException(SR.Format(SR.JsonAttributeAlreadyWritten, JsonGlobals.typeString));
                }

                _isWritingDataTypeAttribute = true;
            }
            else if (localName == JsonGlobals.serverTypeString)
            {
                if (_serverTypeValue != null)
                {
                    throw new XmlException(SR.Format(SR.JsonAttributeAlreadyWritten, JsonGlobals.serverTypeString));
                }

                if ((_dataType != JsonDataType.None) && (_dataType != JsonDataType.Object))
                {
                    throw new XmlException(SR.Format(SR.JsonServerTypeSpecifiedForInvalidDataType,
                        JsonGlobals.serverTypeString, JsonGlobals.typeString, _dataType.ToString().ToLowerInvariant(), JsonGlobals.objectString));
                }

                _isWritingServerTypeAttribute = true;
            }
            else if (localName == JsonGlobals.itemString)
            {
                if (WrittenNameWithMapping)
                {
                    throw new XmlException(SR.Format(SR.JsonAttributeAlreadyWritten, JsonGlobals.itemString));
                }

                if (!IsWritingNameWithMapping)
                {
                    // Don't write attribute with local name "item" if <item> element is not open.
                    // Not providing a better error message because localization deadline has passed.
                    throw new XmlException(SR.JsonEndElementNoOpenNodes);
                }

                _nameState |= NameState.IsWritingNameAttribute;
            }
            else
            {
                throw new ArgumentException(SR.Format(SR.JsonUnexpectedAttributeLocalName, localName), nameof(localName));
            }
        }