diff --git a/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_10_40.java b/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_10_40.java
index 1f2e88d2d..7d2146a69 100644
--- a/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_10_40.java
+++ b/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_10_40.java
@@ -2006,25 +2006,37 @@ public class VersionConvertor_10_40 {
     throw new FHIRException("Unknown type "+src.fhirType());
   }
 
-  public void copyDomainResource(org.hl7.fhir.dstu2.model.DomainResource src, org.hl7.fhir.r4.model.DomainResource tgt) throws FHIRException {
+  private static boolean isExemptExtension(String url, String[] extensionsToIgnore) {
+    boolean ok = false;
+    for (String s : extensionsToIgnore)
+      if (s.equals(url))
+        ok = true;
+    return ok;
+  }
+
+  public void copyDomainResource(org.hl7.fhir.dstu2.model.DomainResource src, org.hl7.fhir.r4.model.DomainResource tgt, String... extensionsToIgnore) throws FHIRException {
     copyResource(src, tgt);
     tgt.setText(convertNarrative(src.getText()));
     for (org.hl7.fhir.dstu2.model.Resource t : src.getContained())
       tgt.addContained(convertResource(t));
     for (org.hl7.fhir.dstu2.model.Extension t : src.getExtension())
-      tgt.addExtension(convertExtension(t));
+      if (!isExemptExtension(t.getUrl(), extensionsToIgnore))
+        tgt.addExtension(convertExtension(t));
     for (org.hl7.fhir.dstu2.model.Extension t : src.getModifierExtension())
-      tgt.addModifierExtension(convertExtension(t));
+      if (!isExemptExtension(t.getUrl(), extensionsToIgnore))
+        tgt.addModifierExtension(convertExtension(t));
   }
-  public void copyDomainResource(org.hl7.fhir.r4.model.DomainResource src, org.hl7.fhir.dstu2.model.DomainResource tgt) throws FHIRException {
+  public void copyDomainResource(org.hl7.fhir.r4.model.DomainResource src, org.hl7.fhir.dstu2.model.DomainResource tgt, String... extensionsToIgnore) throws FHIRException {
     copyResource(src, tgt);
     tgt.setText(convertNarrative(src.getText()));
     for (org.hl7.fhir.r4.model.Resource t : src.getContained())
       tgt.addContained(convertResource(t));
     for (org.hl7.fhir.r4.model.Extension t : src.getExtension())
-      tgt.addExtension(convertExtension(t));
+      if (!isExemptExtension(t.getUrl(), extensionsToIgnore))
+        tgt.addExtension(convertExtension(t));
     for (org.hl7.fhir.r4.model.Extension t : src.getModifierExtension())
-      tgt.addModifierExtension(convertExtension(t));
+      if (!isExemptExtension(t.getUrl(), extensionsToIgnore))
+        tgt.addModifierExtension(convertExtension(t));
   }
 
   public org.hl7.fhir.r4.model.Parameters convertParameters(org.hl7.fhir.dstu2.model.Parameters src) throws FHIRException {
@@ -4215,7 +4227,9 @@ public class VersionConvertor_10_40 {
     tgt.setSoftware(convertConformanceSoftwareComponent(src.getSoftware()));
     tgt.setImplementation(convertConformanceImplementationComponent(src.getImplementation()));
     tgt.setFhirVersion(org.hl7.fhir.r4.model.Enumerations.FHIRVersion.fromCode(src.getFhirVersion()));
-//    tgt.setAcceptUnknown(convertUnknownContentCode(src.getAcceptUnknown()));
+    if (src.hasAcceptUnknown())
+      tgt.addExtension().setUrl("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown").setValue(
+          new org.hl7.fhir.r4.model.CodeType(src.getAcceptUnknownElement().asStringValue()));
     for (org.hl7.fhir.dstu2.model.CodeType t : src.getFormat())
       tgt.addFormat(t.getValue());
 //    for (org.hl7.fhir.dstu2.model.Reference t : src.getProfile())
@@ -4233,7 +4247,7 @@ public class VersionConvertor_10_40 {
     if (src == null || src.isEmpty())
       return null;
     org.hl7.fhir.dstu2.model.Conformance tgt = new org.hl7.fhir.dstu2.model.Conformance();
-    copyDomainResource(src, tgt);
+    copyDomainResource(src, tgt, "http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown");
     tgt.setUrl(src.getUrl());
     tgt.setVersion(src.getVersion());
     tgt.setName(src.getName());
@@ -4254,7 +4268,9 @@ public class VersionConvertor_10_40 {
       tgt.setImplementation(convertConformanceImplementationComponent(src.getImplementation()));
     if (src.hasFhirVersion())
       tgt.setFhirVersion(src.getFhirVersion().toCode());
-//    tgt.setAcceptUnknown(convertUnknownContentCode(src.getAcceptUnknown()));
+    if (src.hasExtension("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown"))
+      tgt.setAcceptUnknown(org.hl7.fhir.dstu2.model.Conformance.UnknownContentCode.fromCode(
+          src.getExtensionByUrl("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown").getValue().primitiveValue()));
     for (org.hl7.fhir.r4.model.CodeType t : src.getFormat())
       tgt.addFormat(t.getValue());
     for (CapabilityStatementRestComponent r : src.getRest())
diff --git a/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_10_50.java b/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_10_50.java
index f093bc64b..8e8e437c4 100644
--- a/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_10_50.java
+++ b/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_10_50.java
@@ -2006,25 +2006,37 @@ public class VersionConvertor_10_50 {
     throw new FHIRException("Unknown type "+src.fhirType());
   }
 
-  public void copyDomainResource(org.hl7.fhir.dstu2.model.DomainResource src, org.hl7.fhir.r5.model.DomainResource tgt) throws FHIRException {
+  private static boolean isExemptExtension(String url, String[] extensionsToIgnore) {
+    boolean ok = false;
+    for (String s : extensionsToIgnore)
+      if (s.equals(url))
+        ok = true;
+    return ok;
+  }
+
+  public void copyDomainResource(org.hl7.fhir.dstu2.model.DomainResource src, org.hl7.fhir.r5.model.DomainResource tgt, String... extensionsToIgnore) throws FHIRException {
     copyResource(src, tgt);
     tgt.setText(convertNarrative(src.getText()));
     for (org.hl7.fhir.dstu2.model.Resource t : src.getContained())
       tgt.addContained(convertResource(t));
     for (org.hl7.fhir.dstu2.model.Extension t : src.getExtension())
-      tgt.addExtension(convertExtension(t));
+      if (!isExemptExtension(t.getUrl(), extensionsToIgnore))
+        tgt.addExtension(convertExtension(t));
     for (org.hl7.fhir.dstu2.model.Extension t : src.getModifierExtension())
-      tgt.addModifierExtension(convertExtension(t));
+      if (!isExemptExtension(t.getUrl(), extensionsToIgnore))
+        tgt.addModifierExtension(convertExtension(t));
   }
-  public void copyDomainResource(org.hl7.fhir.r5.model.DomainResource src, org.hl7.fhir.dstu2.model.DomainResource tgt) throws FHIRException {
+  public void copyDomainResource(org.hl7.fhir.r5.model.DomainResource src, org.hl7.fhir.dstu2.model.DomainResource tgt, String... extensionsToIgnore) throws FHIRException {
     copyResource(src, tgt);
     tgt.setText(convertNarrative(src.getText()));
     for (org.hl7.fhir.r5.model.Resource t : src.getContained())
       tgt.addContained(convertResource(t));
     for (org.hl7.fhir.r5.model.Extension t : src.getExtension())
-      tgt.addExtension(convertExtension(t));
+      if (!isExemptExtension(t.getUrl(), extensionsToIgnore))
+        tgt.addExtension(convertExtension(t));
     for (org.hl7.fhir.r5.model.Extension t : src.getModifierExtension())
-      tgt.addModifierExtension(convertExtension(t));
+      if (!isExemptExtension(t.getUrl(), extensionsToIgnore))
+        tgt.addModifierExtension(convertExtension(t));
   }
 
   public org.hl7.fhir.r5.model.Parameters convertParameters(org.hl7.fhir.dstu2.model.Parameters src) throws FHIRException {
@@ -4219,7 +4231,9 @@ public class VersionConvertor_10_50 {
     tgt.setSoftware(convertConformanceSoftwareComponent(src.getSoftware()));
     tgt.setImplementation(convertConformanceImplementationComponent(src.getImplementation()));
     tgt.setFhirVersion(org.hl7.fhir.r5.model.Enumerations.FHIRVersion.fromCode(src.getFhirVersion()));
-//    tgt.setAcceptUnknown(convertUnknownContentCode(src.getAcceptUnknown()));
+    if (src.hasAcceptUnknown())
+      tgt.addExtension().setUrl("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown").setValue(
+          new org.hl7.fhir.r5.model.CodeType(src.getAcceptUnknownElement().asStringValue()));
     for (org.hl7.fhir.dstu2.model.CodeType t : src.getFormat())
       tgt.addFormat(t.getValue());
 //    for (org.hl7.fhir.dstu2.model.Reference t : src.getProfile())
@@ -4237,7 +4251,7 @@ public class VersionConvertor_10_50 {
     if (src == null || src.isEmpty())
       return null;
     org.hl7.fhir.dstu2.model.Conformance tgt = new org.hl7.fhir.dstu2.model.Conformance();
-    copyDomainResource(src, tgt);
+    copyDomainResource(src, tgt, "http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown");
     tgt.setUrl(src.getUrl());
     tgt.setVersion(src.getVersion());
     tgt.setName(src.getName());
@@ -4258,7 +4272,9 @@ public class VersionConvertor_10_50 {
       tgt.setImplementation(convertConformanceImplementationComponent(src.getImplementation()));
     if (src.hasFhirVersion())
       tgt.setFhirVersion(src.getFhirVersion().toCode());
-//    tgt.setAcceptUnknown(convertUnknownContentCode(src.getAcceptUnknown()));
+    if (src.hasExtension("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown"))
+      tgt.setAcceptUnknown(org.hl7.fhir.dstu2.model.Conformance.UnknownContentCode.fromCode(
+          src.getExtensionByUrl("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown").getValue().primitiveValue()));
     for (org.hl7.fhir.r5.model.CodeType t : src.getFormat())
       tgt.addFormat(t.getValue());
     for (CapabilityStatementRestComponent r : src.getRest())
diff --git a/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_14_40.java b/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_14_40.java
index 809480331..451f22620 100644
--- a/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_14_40.java
+++ b/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_14_40.java
@@ -2258,26 +2258,38 @@ public class VersionConvertor_14_40 {
     throw new FHIRException("Unknown type "+src.fhirType());
   }
 
-  private static void copyDomainResource(org.hl7.fhir.dstu2016may.model.DomainResource src, org.hl7.fhir.r4.model.DomainResource tgt) throws FHIRException {
+  private static boolean isExemptExtension(String url, String[] extensionsToIgnore) {
+    boolean ok = false;
+    for (String s : extensionsToIgnore)
+      if (s.equals(url))
+        ok = true;
+    return ok;
+  }
+
+  private static void copyDomainResource(org.hl7.fhir.dstu2016may.model.DomainResource src, org.hl7.fhir.r4.model.DomainResource tgt, String... extensionsToIgnore) throws FHIRException {
     copyResource(src, tgt);
     tgt.setText(convertNarrative(src.getText()));
     for (org.hl7.fhir.dstu2016may.model.Resource t : src.getContained())
       tgt.addContained(convertResource(t));
     for (org.hl7.fhir.dstu2016may.model.Extension t : src.getExtension())
-      tgt.addExtension(convertExtension(t));
+      if (!isExemptExtension(t.getUrl(), extensionsToIgnore))
+        tgt.addExtension(convertExtension(t));
     for (org.hl7.fhir.dstu2016may.model.Extension t : src.getModifierExtension())
-      tgt.addModifierExtension(convertExtension(t));
+      if (!isExemptExtension(t.getUrl(), extensionsToIgnore))
+        tgt.addModifierExtension(convertExtension(t));
   }
-  private static void copyDomainResource(org.hl7.fhir.r4.model.DomainResource src, org.hl7.fhir.dstu2016may.model.DomainResource tgt) throws FHIRException {
+  private static void copyDomainResource(org.hl7.fhir.r4.model.DomainResource src, org.hl7.fhir.dstu2016may.model.DomainResource tgt, String... extensionsToIgnore) throws FHIRException {
     copyResource(src, tgt);
     if (src.hasText())
       tgt.setText(convertNarrative(src.getText()));
     for (org.hl7.fhir.r4.model.Resource t : src.getContained())
       tgt.addContained(convertResource(t));
     for (org.hl7.fhir.r4.model.Extension t : src.getExtension())
-      tgt.addExtension(convertExtension(t));
+      if (!isExemptExtension(t.getUrl(), extensionsToIgnore))
+        tgt.addExtension(convertExtension(t));
     for (org.hl7.fhir.r4.model.Extension t : src.getModifierExtension())
-      tgt.addModifierExtension(convertExtension(t));
+      if (!isExemptExtension(t.getUrl(), extensionsToIgnore))
+        tgt.addModifierExtension(convertExtension(t));
   }
   public static org.hl7.fhir.r4.model.Parameters convertParameters(org.hl7.fhir.dstu2016may.model.Parameters src) throws FHIRException {
     if (src == null || src.isEmpty())
@@ -3402,7 +3414,9 @@ public class VersionConvertor_14_40 {
     tgt.setSoftware(convertConformanceSoftwareComponent(src.getSoftware()));
     tgt.setImplementation(convertConformanceImplementationComponent(src.getImplementation()));
     tgt.setFhirVersion(org.hl7.fhir.r4.model.Enumerations.FHIRVersion.fromCode(src.getFhirVersion()));
-//    tgt.setAcceptUnknown(convertUnknownContentCode(src.getAcceptUnknown()));
+    if (src.hasAcceptUnknown())
+      tgt.addExtension().setUrl("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown").setValue(
+          new org.hl7.fhir.r4.model.CodeType(src.getAcceptUnknownElement().asStringValue()));
     for (org.hl7.fhir.dstu2016may.model.CodeType t : src.getFormat())
       tgt.addFormat(t.getValue());
 //    for (org.hl7.fhir.dstu2016may.model.Reference t : src.getProfile())
@@ -3432,7 +3446,7 @@ public class VersionConvertor_14_40 {
     if (src == null || src.isEmpty())
       return null;
     org.hl7.fhir.dstu2016may.model.Conformance tgt = new org.hl7.fhir.dstu2016may.model.Conformance();
-    copyDomainResource(src, tgt);
+    copyDomainResource(src, tgt, "http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown");
     if (src.hasUrl())
       tgt.setUrl(src.getUrl());
     if (src.hasVersion())
@@ -3463,7 +3477,9 @@ public class VersionConvertor_14_40 {
     tgt.setSoftware(convertConformanceSoftwareComponent(src.getSoftware()));
     tgt.setImplementation(convertConformanceImplementationComponent(src.getImplementation()));
     tgt.setFhirVersion(src.getFhirVersion().toCode());
-//    tgt.setAcceptUnknown(convertUnknownContentCode(src.getAcceptUnknown()));
+    if (src.hasExtension("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown"))
+      tgt.setAcceptUnknown(org.hl7.fhir.dstu2016may.model.Conformance.UnknownContentCode.fromCode(
+          src.getExtensionByUrl("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown").getValue().primitiveValue()));
     for (org.hl7.fhir.r4.model.CodeType t : src.getFormat())
       tgt.addFormat(t.getValue());
     for (CapabilityStatementRestComponent r : src.getRest())
diff --git a/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_14_50.java b/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_14_50.java
index 9b13f76f0..fa081f542 100644
--- a/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_14_50.java
+++ b/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_14_50.java
@@ -2256,26 +2256,38 @@ public class VersionConvertor_14_50 {
     throw new FHIRException("Unknown type "+src.fhirType());
   }
 
-  private static void copyDomainResource(org.hl7.fhir.dstu2016may.model.DomainResource src, org.hl7.fhir.r5.model.DomainResource tgt) throws FHIRException {
+  private static boolean isExemptExtension(String url, String[] extensionsToIgnore) {
+    boolean ok = false;
+    for (String s : extensionsToIgnore)
+      if (s.equals(url))
+        ok = true;
+    return ok;
+  }
+
+  private static void copyDomainResource(org.hl7.fhir.dstu2016may.model.DomainResource src, org.hl7.fhir.r5.model.DomainResource tgt, String... extensionsToIgnore) throws FHIRException {
     copyResource(src, tgt);
     tgt.setText(convertNarrative(src.getText()));
     for (org.hl7.fhir.dstu2016may.model.Resource t : src.getContained())
       tgt.addContained(convertResource(t));
     for (org.hl7.fhir.dstu2016may.model.Extension t : src.getExtension())
-      tgt.addExtension(convertExtension(t));
+      if (!isExemptExtension(t.getUrl(), extensionsToIgnore))
+        tgt.addExtension(convertExtension(t));
     for (org.hl7.fhir.dstu2016may.model.Extension t : src.getModifierExtension())
-      tgt.addModifierExtension(convertExtension(t));
+      if (!isExemptExtension(t.getUrl(), extensionsToIgnore))
+        tgt.addModifierExtension(convertExtension(t));
   }
-  private static void copyDomainResource(org.hl7.fhir.r5.model.DomainResource src, org.hl7.fhir.dstu2016may.model.DomainResource tgt) throws FHIRException {
+  private static void copyDomainResource(org.hl7.fhir.r5.model.DomainResource src, org.hl7.fhir.dstu2016may.model.DomainResource tgt, String... extensionsToIgnore) throws FHIRException {
     copyResource(src, tgt);
     if (src.hasText())
       tgt.setText(convertNarrative(src.getText()));
     for (org.hl7.fhir.r5.model.Resource t : src.getContained())
       tgt.addContained(convertResource(t));
     for (org.hl7.fhir.r5.model.Extension t : src.getExtension())
-      tgt.addExtension(convertExtension(t));
+      if (!isExemptExtension(t.getUrl(), extensionsToIgnore))
+        tgt.addExtension(convertExtension(t));
     for (org.hl7.fhir.r5.model.Extension t : src.getModifierExtension())
-      tgt.addModifierExtension(convertExtension(t));
+      if (!isExemptExtension(t.getUrl(), extensionsToIgnore))
+        tgt.addModifierExtension(convertExtension(t));
   }
   public static org.hl7.fhir.r5.model.Parameters convertParameters(org.hl7.fhir.dstu2016may.model.Parameters src) throws FHIRException {
     if (src == null || src.isEmpty())
@@ -3404,7 +3416,9 @@ public class VersionConvertor_14_50 {
     tgt.setSoftware(convertConformanceSoftwareComponent(src.getSoftware()));
     tgt.setImplementation(convertConformanceImplementationComponent(src.getImplementation()));
     tgt.setFhirVersion(org.hl7.fhir.r5.model.Enumerations.FHIRVersion.fromCode(src.getFhirVersion()));
-//    tgt.setAcceptUnknown(convertUnknownContentCode(src.getAcceptUnknown()));
+    if (src.hasAcceptUnknown())
+      tgt.addExtension().setUrl("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown").setValue(
+          new org.hl7.fhir.r5.model.CodeType(src.getAcceptUnknownElement().asStringValue()));
     for (org.hl7.fhir.dstu2016may.model.CodeType t : src.getFormat())
       tgt.addFormat(t.getValue());
 //    for (org.hl7.fhir.dstu2016may.model.Reference t : src.getProfile())
@@ -3434,7 +3448,7 @@ public class VersionConvertor_14_50 {
     if (src == null || src.isEmpty())
       return null;
     org.hl7.fhir.dstu2016may.model.Conformance tgt = new org.hl7.fhir.dstu2016may.model.Conformance();
-    copyDomainResource(src, tgt);
+    copyDomainResource(src, tgt, "http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown");
     if (src.hasUrl())
       tgt.setUrl(src.getUrl());
     if (src.hasVersion())
@@ -3465,7 +3479,9 @@ public class VersionConvertor_14_50 {
     tgt.setSoftware(convertConformanceSoftwareComponent(src.getSoftware()));
     tgt.setImplementation(convertConformanceImplementationComponent(src.getImplementation()));
     tgt.setFhirVersion(src.getFhirVersion().toCode());
-//    tgt.setAcceptUnknown(convertUnknownContentCode(src.getAcceptUnknown()));
+    if (src.hasExtension("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown"))
+      tgt.setAcceptUnknown(org.hl7.fhir.dstu2016may.model.Conformance.UnknownContentCode.fromCode(
+          src.getExtensionByUrl("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown").getValue().primitiveValue()));
     for (org.hl7.fhir.r5.model.CodeType t : src.getFormat())
       tgt.addFormat(t.getValue());
     for (CapabilityStatementRestComponent r : src.getRest())
diff --git a/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_30_40.java b/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_30_40.java
index b2a22eae4..93ca745a8 100644
--- a/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_30_40.java
+++ b/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_30_40.java
@@ -2949,27 +2949,39 @@ public class VersionConvertor_30_40 {
     throw new FHIRException("Unknown type "+src.fhirType());
   }
 
-  private static void copyDomainResource(org.hl7.fhir.dstu3.model.DomainResource src, org.hl7.fhir.r4.model.DomainResource tgt) throws FHIRException {
+  private static boolean isExemptExtension(String url, String[] extensionsToIgnore) {
+    boolean ok = false;
+    for (String s : extensionsToIgnore)
+      if (s.equals(url))
+        ok = true;
+    return ok;
+  }
+
+  private static void copyDomainResource(org.hl7.fhir.dstu3.model.DomainResource src, org.hl7.fhir.r4.model.DomainResource tgt, String... extensionsToIgnore) throws FHIRException {
     copyResource(src, tgt);
     if (src.hasText())
       tgt.setText(convertNarrative(src.getText()));
     for (org.hl7.fhir.dstu3.model.Resource t1 : src.getContained())
       tgt.addContained(convertResource(t1, false));
     for (org.hl7.fhir.dstu3.model.Extension t2 : src.getExtension())
-      tgt.addExtension(convertExtension(t2));
+      if (!isExemptExtension(t2.getUrl(), extensionsToIgnore))
+        tgt.addExtension(convertExtension(t2));
     for (org.hl7.fhir.dstu3.model.Extension t3 : src.getModifierExtension())
-      tgt.addModifierExtension(convertExtension(t3));
+      if (!isExemptExtension(t3.getUrl(), extensionsToIgnore))
+        tgt.addModifierExtension(convertExtension(t3));
   }
-  private static void copyDomainResource(org.hl7.fhir.r4.model.DomainResource src, org.hl7.fhir.dstu3.model.DomainResource tgt) throws FHIRException {
+  private static void copyDomainResource(org.hl7.fhir.r4.model.DomainResource src, org.hl7.fhir.dstu3.model.DomainResource tgt, String... extensionsToIgnore) throws FHIRException {
     copyResource(src, tgt);
     if (src.hasText())
       tgt.setText(convertNarrative(src.getText()));
     for (org.hl7.fhir.r4.model.Resource t1 : src.getContained())
       tgt.addContained(convertResource(t1, false));
     for (org.hl7.fhir.r4.model.Extension t2 : src.getExtension())
-      tgt.addExtension(convertExtension(t2));
+      if (!isExemptExtension(t2.getUrl(), extensionsToIgnore))
+        tgt.addExtension(convertExtension(t2));
     for (org.hl7.fhir.r4.model.Extension t3 : src.getModifierExtension())
-      tgt.addModifierExtension(convertExtension(t3));
+      if (!isExemptExtension(t3.getUrl(), extensionsToIgnore))
+        tgt.addModifierExtension(convertExtension(t3));
   }
   public static org.hl7.fhir.r4.model.Parameters convertParameters(org.hl7.fhir.dstu3.model.Parameters src) throws FHIRException {
     if (src == null)
@@ -4680,8 +4692,9 @@ public class VersionConvertor_30_40 {
       tgt.setImplementation(convertCapabilityStatementImplementationComponent(src.getImplementation()));
     if (src.hasFhirVersion())
       tgt.setFhirVersion(org.hl7.fhir.r4.model.Enumerations.FHIRVersion.fromCode(src.getFhirVersion()));
-//    if (src.hasAcceptUnknown())
-//      tgt.setAcceptUnknown(convertUnknownContentCode(src.getAcceptUnknown()));
+    if (src.hasAcceptUnknown())
+      tgt.addExtension().setUrl("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown").setValue(
+          new org.hl7.fhir.r4.model.CodeType(src.getAcceptUnknownElement().asStringValue()));
     for (org.hl7.fhir.dstu3.model.CodeType t : src.getFormat())
       tgt.addFormat(t.getValue());
     for (org.hl7.fhir.dstu3.model.CodeType t : src.getPatchFormat())
@@ -4704,7 +4717,7 @@ public class VersionConvertor_30_40 {
     if (src == null)
       return null;
     org.hl7.fhir.dstu3.model.CapabilityStatement tgt = new org.hl7.fhir.dstu3.model.CapabilityStatement();
-    copyDomainResource(src, tgt);
+    copyDomainResource(src, tgt, "http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown");
     if (src.hasUrl())
       tgt.setUrl(src.getUrl());
     if (src.hasVersion())
@@ -4743,8 +4756,9 @@ public class VersionConvertor_30_40 {
       tgt.setImplementation(convertCapabilityStatementImplementationComponent(src.getImplementation()));
     if (src.hasFhirVersion())
       tgt.setFhirVersion(src.getFhirVersion().toCode());
-//    if (src.hasAcceptUnknown())
-//      tgt.setAcceptUnknown(convertUnknownContentCode(src.getAcceptUnknown()));
+    if (src.hasExtension("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown"))
+      tgt.setAcceptUnknown(org.hl7.fhir.dstu3.model.CapabilityStatement.UnknownContentCode.fromCode(
+          src.getExtensionByUrl("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown").getValue().primitiveValue()));
     for (org.hl7.fhir.r4.model.CodeType t : src.getFormat())
       tgt.addFormat(t.getValue());
     for (org.hl7.fhir.r4.model.CodeType t : src.getPatchFormat())
diff --git a/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_30_50.java b/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_30_50.java
index 3f4d0a7c7..1ed4f0cd5 100644
--- a/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_30_50.java
+++ b/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/VersionConvertor_30_50.java
@@ -2932,22 +2932,23 @@ public class VersionConvertor_30_50 {
     for (org.hl7.fhir.dstu3.model.Resource t1 : src.getContained())
       tgt.addContained(convertResource(t1, false));
     for (org.hl7.fhir.dstu3.model.Extension t2 : src.getExtension()) {
-      boolean ok = true;
-      for (String s : extensionsToIgnore)
-        if (s.equals(t2.getUrl()))
-          ok = false;
-      if (ok)
+      if (!isExemptExtension(t2.getUrl(), extensionsToIgnore))
         tgt.addExtension(convertExtension(t2));
     }
     for (org.hl7.fhir.dstu3.model.Extension t3 : src.getModifierExtension()) {
-      boolean ok = true;
-      for (String s : extensionsToIgnore)
-        if (s.equals(t3.getUrl()))
-          ok = false;
-      if (ok)
+      if (!isExemptExtension(t3.getUrl(), extensionsToIgnore))
         tgt.addModifierExtension(convertExtension(t3));
     }
   }
+  
+  private static boolean isExemptExtension(String url, String[] extensionsToIgnore) {
+    boolean ok = false;
+    for (String s : extensionsToIgnore)
+      if (s.equals(url))
+        ok = true;
+    return ok;
+  }
+
   private static void copyDomainResource(org.hl7.fhir.r5.model.DomainResource src, org.hl7.fhir.dstu3.model.DomainResource tgt, String... extensionsToIgnore) throws FHIRException {
     copyResource(src, tgt);
     if (src.hasText())
@@ -2955,20 +2956,12 @@ public class VersionConvertor_30_50 {
     for (org.hl7.fhir.r5.model.Resource t1 : src.getContained())
       tgt.addContained(convertResource(t1, false));
     for (org.hl7.fhir.r5.model.Extension t2 : src.getExtension()) {
-      boolean ok = true;
-      for (String s : extensionsToIgnore)
-        if (s.equals(t2.getUrl()))
-          ok = false;
-      if (ok)
+      if (!isExemptExtension(t2.getUrl(), extensionsToIgnore))
         tgt.addExtension(convertExtension(t2));
       }
     for (org.hl7.fhir.r5.model.Extension t3 : src.getModifierExtension()) {
-      boolean ok = true;
-      for (String s : extensionsToIgnore)
-        if (s.equals(t3.getUrl()))
-          ok = false;
-      if (ok)
-      tgt.addModifierExtension(convertExtension(t3));
+      if (!isExemptExtension(t3.getUrl(), extensionsToIgnore))
+        tgt.addModifierExtension(convertExtension(t3));
     }
   }
   public static org.hl7.fhir.r5.model.Parameters convertParameters(org.hl7.fhir.dstu3.model.Parameters src) throws FHIRException {
@@ -4680,8 +4673,9 @@ public class VersionConvertor_30_50 {
       tgt.setImplementation(convertCapabilityStatementImplementationComponent(src.getImplementation()));
     if (src.hasFhirVersion())
       tgt.setFhirVersion(org.hl7.fhir.r5.model.Enumerations.FHIRVersion.fromCode(src.getFhirVersion()));
-//    if (src.hasAcceptUnknown())
-//      tgt.setAcceptUnknown(convertUnknownContentCode(src.getAcceptUnknown()));
+    if (src.hasAcceptUnknown())
+      tgt.addExtension().setUrl("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown").setValue(
+          new org.hl7.fhir.r5.model.CodeType(src.getAcceptUnknownElement().asStringValue()));
     for (org.hl7.fhir.dstu3.model.CodeType t : src.getFormat())
       tgt.addFormat(t.getValue());
     for (org.hl7.fhir.dstu3.model.CodeType t : src.getPatchFormat())
@@ -4704,7 +4698,7 @@ public class VersionConvertor_30_50 {
     if (src == null)
       return null;
     org.hl7.fhir.dstu3.model.CapabilityStatement tgt = new org.hl7.fhir.dstu3.model.CapabilityStatement();
-    copyDomainResource(src, tgt);
+    copyDomainResource(src, tgt, "http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown");
     if (src.hasUrl())
       tgt.setUrl(src.getUrl());
     if (src.hasVersion())
@@ -4743,8 +4737,9 @@ public class VersionConvertor_30_50 {
       tgt.setImplementation(convertCapabilityStatementImplementationComponent(src.getImplementation()));
     if (src.hasFhirVersion())
       tgt.setFhirVersion(src.getFhirVersion().toCode());
-//    if (src.hasAcceptUnknown())
-//      tgt.setAcceptUnknown(convertUnknownContentCode(src.getAcceptUnknown()));
+    if (src.hasExtension("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown"))
+      tgt.setAcceptUnknown(org.hl7.fhir.dstu3.model.CapabilityStatement.UnknownContentCode.fromCode(
+          src.getExtensionByUrl("http://hl7.org/fhir/3.0/StructureDefinition/extension-CapabilityStatement.acceptUnknown").getValue().primitiveValue()));
     for (org.hl7.fhir.r5.model.CodeType t : src.getFormat())
       tgt.addFormat(t.getValue());
     for (org.hl7.fhir.r5.model.CodeType t : src.getPatchFormat())
diff --git a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/ToolingExtensions.java b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/ToolingExtensions.java
index 4d294d497..a58c3fa8b 100644
--- a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/ToolingExtensions.java
+++ b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/ToolingExtensions.java
@@ -81,6 +81,7 @@ import org.hl7.fhir.r5.model.Questionnaire.QuestionnaireItemType;
 import org.hl7.fhir.r5.model.StringType;
 import org.hl7.fhir.r5.model.Type;
 import org.hl7.fhir.r5.model.UriType;
+import org.hl7.fhir.r5.model.UrlType;
 import org.hl7.fhir.r5.model.ValueSet.ConceptReferenceComponent;
 import org.hl7.fhir.r5.model.ValueSet.ConceptSetComponent;
 import org.hl7.fhir.utilities.StandardsStatus;
@@ -816,5 +817,23 @@ public class ToolingExtensions {
 //    return hasExtension(cs, EXT_OID);
 //  }
 //  
+  public static void addUrlExtension(Element e, String url, String content) {
+    if (!StringUtils.isBlank(content)) {
+      Extension ex = getExtension(e, url);
+      if (ex != null)
+        ex.setValue(new CodeType(content));
+      else
+        e.getExtension().add(Factory.newExtension(url, new UrlType(content), true));   
+    }
+  }
+
+  public static void addUrlExtension(DomainResource dr, String url, String value) {
+    Extension ex = getExtension(dr, url);
+    if (ex != null)
+      ex.setValue(new CodeType(value));
+    else
+      dr.getExtension().add(Factory.newExtension(url, new UrlType(value), true));   
+  }
+
   
 }