First draft of this PR, all unit tests run.

src/Hl7.Fhir.Base/Model/Generated/Attachment.cs

@@ -180,7 +180,7 @@ public Hl7.Fhir.Model.PrimitiveType UrlElement
     [IgnoreDataMember]
     public string UrlUri
     {
-      get { return UrlElement != null ? ((Hl7.Fhir.Model.FhirUri)UrlElement).Value : null; }
+      get { return UrlElement != null ? ((IValue<string>)UrlElement).Value : null; }
       set
       {
         if (value == null)
@@ -198,7 +198,7 @@ public string UrlUri
     [IgnoreDataMember]
     public string Url
     {
-      get { return UrlElement != null ? ((Hl7.Fhir.Model.FhirUrl)UrlElement).Value : null; }
+      get { return UrlElement != null ? ((IValue<string>)UrlElement).Value : null; }
       set
       {
         if (value == null)

src/Hl7.Fhir.Base/Model/Generated/Bundle.cs

@@ -979,7 +979,7 @@ public Hl7.Fhir.Model.PrimitiveType RelationElement
       [IgnoreDataMember]
       public string RelationString
       {
-        get { return RelationElement != null ? ((Hl7.Fhir.Model.FhirString)RelationElement).Value : null; }
+        get { return RelationElement != null ? ((IValue<string>)RelationElement).Value : null; }
         set
         {
           if (value == null)
@@ -997,7 +997,7 @@ public string RelationString
       [IgnoreDataMember]
       public string Relation
       {
-        get { return RelationElement != null ? ((Hl7.Fhir.Model.Code)RelationElement).Value : null; }
+        get { return RelationElement != null ? ((IValue<string>)RelationElement).Value : null; }
         set
         {
           if (value == null)

src/Hl7.Fhir.Base/Serialization/BaseFhirJsonPocoDeserializer.cs

@@ -782,18 +782,6 @@ string typeName()
                 bool isInteger64()
                     => fhirType == typeof(Integer64);
             }
-
-            // Validation is now done using POCO validation, so have removed it here.
-            // Keep code around in case I make my mind up before publication.
-            //static (object?, FhirJsonException?) readEnum(ref Utf8JsonReader reader, Type enumType)
-            //{
-            //    var contents = reader.GetString()!;
-            //    var enumValue = EnumUtility.ParseLiteral(contents, enumType);
-
-            //    return enumValue is not null
-            //        ? (contents, null)
-            //        : (contents, ERR.CODED_VALUE_NOT_IN_ENUM.With(ref reader, contents, EnumUtility.GetName(enumType)));
-            //}
         }
 
         private static (object?, FhirJsonException) unexpectedToken(ref Utf8JsonReader reader, string instancePath, string? value, string expected, string actual) =>

src/Hl7.Fhir.Base/Serialization/FhirJsonException.cs

@@ -45,17 +45,19 @@ public class FhirJsonException : ExtendedCodedException
         public const string RESOURCE_TYPE_NOT_A_RESOURCE_CODE = "JSON117";
         public const string UNKNOWN_PROPERTY_FOUND_CODE = "JSON118";
 
-        [Obsolete("This issue is no longer raised as it is now allowed to use `resourceType` as the name of an element.")]
-        public const string RESOURCETYPE_UNEXPECTED_CODE = "JSON119";
+        //[Obsolete("This issue is no longer raised as it is now allowed to use `resourceType` as the name of an element.")]
+        //public const string RESOURCETYPE_UNEXPECTED_CODE = "JSON119";
         public const string OBJECTS_CANNOT_BE_EMPTY_CODE = "JSON120";
         public const string ARRAYS_CANNOT_BE_EMPTY_CODE = "JSON121";
         public const string LONG_CANNOT_BE_PARSED_CODE = "JSON122";
         public const string LONG_INCORRECT_FORMAT_CODE = "JSON123";
 
-        [Obsolete("According to the latest updates of the Json format, primitive arrays of different sizes are no longer considered an error.")]
-        public const string PRIMITIVE_ARRAYS_INCOMPAT_SIZE_CODE = "JSON122";
+        //[Obsolete("According to the latest updates of the Json format, primitive arrays of different sizes are no longer considered an error.")]
+        //public const string PRIMITIVE_ARRAYS_INCOMPAT_SIZE_CODE = "JSON122";
 
         public const string PRIMITIVE_ARRAYS_ONLY_NULL_CODE = "JSON125";
+
+        // Cannot happen anymore since 6.0 since the simple values Element.id and Extension.url are gone.
         //public const string INCOMPATIBLE_SIMPLE_VALUE_CODE = "JSON126";
         public const string PROPERTY_MAY_NOT_BE_EMPTY_CODE = "JSON127";
 
@@ -107,8 +109,8 @@ public class FhirJsonException : ExtendedCodedException
 
         // The serialization contained a superfluous 'resourceType' property, but we have read all data anyway.
         // Note, this is no longer considered an error, since there are Resources using an element named "resourceType" (Subscription.filterBy for example).
-        [Obsolete("This issue is no longer raised as it is now allowed to use `resourceType` as the name of an element.")]
-        internal static FhirJsonException RESOURCETYPE_UNEXPECTED(ref Utf8JsonReader reader, string instancePath) => Initialize(ref reader, instancePath, RESOURCETYPE_UNEXPECTED_CODE, "The 'resourceType' property should only be used in resources.", OO_Sev.Warning, OO_Typ.Structure);
+        //[Obsolete("This issue is no longer raised as it is now allowed to use `resourceType` as the name of an element.")]
+        //internal static FhirJsonException RESOURCETYPE_UNEXPECTED(ref Utf8JsonReader reader, string instancePath) => Initialize(ref reader, instancePath, RESOURCETYPE_UNEXPECTED_CODE, "The 'resourceType' property should only be used in resources.", OO_Sev.Warning, OO_Typ.Structure);
 
         // Empty objects and arrays can be ignored without discarding data
         internal static FhirJsonException OBJECTS_CANNOT_BE_EMPTY(ref Utf8JsonReader reader, string instancePath) => Initialize(ref reader, instancePath, OBJECTS_CANNOT_BE_EMPTY_CODE, "An object needs to have at least one property.", OO_Sev.Warning, OO_Typ.Structure);
@@ -137,10 +139,10 @@ public class FhirJsonException : ExtendedCodedException
             LONG_INCORRECT_FORMAT_CODE,
             EXPECTED_START_OF_ARRAY_CODE,
             USE_OF_UNDERSCORE_ILLEGAL_CODE,
-            RESOURCETYPE_UNEXPECTED_CODE,
+          //  RESOURCETYPE_UNEXPECTED_CODE,
             OBJECTS_CANNOT_BE_EMPTY_CODE,
             ARRAYS_CANNOT_BE_EMPTY_CODE,
-            PRIMITIVE_ARRAYS_INCOMPAT_SIZE_CODE,
+          //  PRIMITIVE_ARRAYS_INCOMPAT_SIZE_CODE,
             PRIMITIVE_ARRAYS_ONLY_NULL_CODE,
             PROPERTY_MAY_NOT_BE_EMPTY_CODE,
             DUPLICATE_ARRAY_CODE

src/Hl7.Fhir.Conformance/Model/Generated/CapabilityStatement.cs

@@ -602,7 +602,7 @@ public Hl7.Fhir.Model.PrimitiveType DescriptionElement
       [IgnoreDataMember]
       public string DescriptionString
       {
-        get { return DescriptionElement != null ? ((Hl7.Fhir.Model.FhirString)DescriptionElement).Value : null; }
+        get { return DescriptionElement != null ? ((IValue<string>)DescriptionElement).Value : null; }
         set
         {
           if (value == null)
@@ -620,7 +620,7 @@ public string DescriptionString
       [IgnoreDataMember]
       public string Description
       {
-        get { return DescriptionElement != null ? ((Hl7.Fhir.Model.Markdown)DescriptionElement).Value : null; }
+        get { return DescriptionElement != null ? ((IValue<string>)DescriptionElement).Value : null; }
         set
         {
           if (value == null)

src/Hl7.Fhir.Conformance/Model/Generated/ElementDefinition.cs

@@ -1431,7 +1431,7 @@ public Hl7.Fhir.Model.PrimitiveType RequirementsElement
       [IgnoreDataMember]
       public string RequirementsString
       {
-        get { return RequirementsElement != null ? ((Hl7.Fhir.Model.FhirString)RequirementsElement).Value : null; }
+        get { return RequirementsElement != null ? ((IValue<string>)RequirementsElement).Value : null; }
         set
         {
           if (value == null)
@@ -1449,7 +1449,7 @@ public string RequirementsString
       [IgnoreDataMember]
       public string Requirements
       {
-        get { return RequirementsElement != null ? ((Hl7.Fhir.Model.Markdown)RequirementsElement).Value : null; }
+        get { return RequirementsElement != null ? ((IValue<string>)RequirementsElement).Value : null; }
         set
         {
           if (value == null)
@@ -1879,7 +1879,7 @@ public Hl7.Fhir.Model.PrimitiveType DescriptionElement
       [IgnoreDataMember]
       public string DescriptionString
       {
-        get { return DescriptionElement != null ? ((Hl7.Fhir.Model.FhirString)DescriptionElement).Value : null; }
+        get { return DescriptionElement != null ? ((IValue<string>)DescriptionElement).Value : null; }
         set
         {
           if (value == null)
@@ -1897,7 +1897,7 @@ public string DescriptionString
       [IgnoreDataMember]
       public string Description
       {
-        get { return DescriptionElement != null ? ((Hl7.Fhir.Model.Markdown)DescriptionElement).Value : null; }
+        get { return DescriptionElement != null ? ((IValue<string>)DescriptionElement).Value : null; }
         set
         {
           if (value == null)
@@ -2533,7 +2533,7 @@ public Hl7.Fhir.Model.PrimitiveType CommentElement
       [IgnoreDataMember]
       public string CommentString
       {
-        get { return CommentElement != null ? ((Hl7.Fhir.Model.FhirString)CommentElement).Value : null; }
+        get { return CommentElement != null ? ((IValue<string>)CommentElement).Value : null; }
         set
         {
           if (value == null)
@@ -2551,7 +2551,7 @@ public string CommentString
       [IgnoreDataMember]
       public string Comment
       {
-        get { return CommentElement != null ? ((Hl7.Fhir.Model.Markdown)CommentElement).Value : null; }
+        get { return CommentElement != null ? ((IValue<string>)CommentElement).Value : null; }
         set
         {
           if (value == null)

src/Hl7.Fhir.STU3/Model/Generated/CapabilityStatement.cs

@@ -640,54 +640,31 @@ public partial class ImplementationComponent : Hl7.Fhir.Model.BackboneElement
       /// <summary>
       /// Describes this specific instance.
       /// </summary>
-      /// <remarks>
-      /// The type of this element has changed over time. Make sure to use Hl7.Fhir.Model.FhirString in STU3, R4 and R4B, Hl7.Fhir.Model.Markdown starting from R5.
-      /// </remarks>
       [FhirElement("description", InSummary=true, Order=40)]
-      [DeclaredType(Type = typeof(Hl7.Fhir.Model.FhirString), Since = FhirRelease.STU3)]
-      [DeclaredType(Type = typeof(Hl7.Fhir.Model.Markdown), Since = FhirRelease.R5)]
       [Cardinality(Min=1,Max=1)]
       [DataMember]
-      public Hl7.Fhir.Model.PrimitiveType DescriptionElement
+      public Hl7.Fhir.Model.FhirString DescriptionElement
       {
         get { return _DescriptionElement; }
         set { _DescriptionElement = value; OnPropertyChanged("DescriptionElement"); }
       }
 
-      private Hl7.Fhir.Model.PrimitiveType _DescriptionElement;
-
-      /// <summary>
-      /// Describes this specific instance. Use this property in STU3, R4 and R4B.
-      /// </summary>
-      /// <remarks>This uses the native .NET datatype, rather than the FHIR equivalent</remarks>
-      [IgnoreDataMember]
-      public string DescriptionString
-      {
-        get { return DescriptionElement != null ? ((Hl7.Fhir.Model.FhirString)DescriptionElement).Value : null; }
-        set
-        {
-          if (value == null)
-            DescriptionElement = null;
-          else
-            DescriptionElement = new Hl7.Fhir.Model.FhirString(value);
-          OnPropertyChanged("DescriptionString");
-        }
-      }
+      private Hl7.Fhir.Model.FhirString _DescriptionElement;
 
       /// <summary>
-      /// Describes this specific instance. Use this property starting from R5.
+      /// Describes this specific instance
       /// </summary>
       /// <remarks>This uses the native .NET datatype, rather than the FHIR equivalent</remarks>
       [IgnoreDataMember]
       public string Description
       {
-        get { return DescriptionElement != null ? ((Hl7.Fhir.Model.Markdown)DescriptionElement).Value : null; }
+        get { return DescriptionElement != null ? DescriptionElement.Value : null; }
         set
         {
           if (value == null)
             DescriptionElement = null;
           else
-            DescriptionElement = new Hl7.Fhir.Model.Markdown(value);
+            DescriptionElement = new Hl7.Fhir.Model.FhirString(value);
           OnPropertyChanged("Description");
         }
       }
@@ -733,7 +710,7 @@ public override IDeepCopyable CopyTo(IDeepCopyable other)
         }
 
         base.CopyTo(dest);
-        if(DescriptionElement != null) dest.DescriptionElement = (Hl7.Fhir.Model.PrimitiveType)DescriptionElement.DeepCopy();
+        if(DescriptionElement != null) dest.DescriptionElement = (Hl7.Fhir.Model.FhirString)DescriptionElement.DeepCopy();
         if(UrlElement != null) dest.UrlElement = (Hl7.Fhir.Model.FhirUri)UrlElement.DeepCopy();
         return dest;
       }
@@ -789,7 +766,7 @@ internal protected override Base SetValue(string key, object value)
         switch (key)
         {
           case "description":
-            DescriptionElement = (Hl7.Fhir.Model.PrimitiveType)value;
+            DescriptionElement = (Hl7.Fhir.Model.FhirString)value;
             return this;
           case "url":
             UrlElement = (Hl7.Fhir.Model.FhirUri)value;