diff --git a/r5/capabilitystatement-import/CapabilityStatement-1.xml b/r5/capabilitystatement-import/CapabilityStatement-1.xml
index 9f553157..b26afb71 100644
--- a/r5/capabilitystatement-import/CapabilityStatement-1.xml
+++ b/r5/capabilitystatement-import/CapabilityStatement-1.xml
@@ -408,7 +408,11 @@
     </operation>
   </rest>
   <messaging>
-    <reliableCache value="10"/>
+    <reliableCache value="10">
+      <extension url="http://hl7.org/fhir/StructureDefinition/capabilitystatement-expectation">
+        <valueCode value="SHOULD"/>
+      </extension>    
+    </reliableCache>
     <documentation value="Whatever"/>
     <supportedMessage>
       <extension url="http://hl7.org/fhir/StructureDefinition/capabilitystatement-expectation">
diff --git a/r5/capabilitystatement-import/CapabilityStatement-2.xml b/r5/capabilitystatement-import/CapabilityStatement-2.xml
index 56e58dda..69d354c5 100644
--- a/r5/capabilitystatement-import/CapabilityStatement-2.xml
+++ b/r5/capabilitystatement-import/CapabilityStatement-2.xml
@@ -432,7 +432,11 @@
       </protocol>
       <address value="http://example.org/endpoint2"/>
     </endpoint>
-    <reliableCache value="20"/>
+    <reliableCache value="20">
+      <extension url="http://hl7.org/fhir/StructureDefinition/capabilitystatement-expectation">
+        <valueCode value="SHALL"/>
+      </extension>
+    </reliableCache>
     <documentation value="Whatever"/>
     <supportedMessage>
       <extension url="http://hl7.org/fhir/StructureDefinition/capabilitystatement-expectation">
diff --git a/validator/manifest.json b/validator/manifest.json
index a361945d..2e37877f 100644
--- a/validator/manifest.json
+++ b/validator/manifest.json
@@ -7,6 +7,7 @@
     " * 'use-test': set to false and the test will be ignored",
     " * 'version': the version being validated. values: 1.0, 1.4, 3.0, 4.0. If no version specified, that means current R5",
     " * 'assumeValidRestReferences' : default = false",
+    " * 'strictIdentifierSystems' : default = false",
     " * 'allowed-extension-domain' : Extension URls from this domain are ok",
     " * 'best-practice': How to treat best practice warnings. missing: ignored, else one of Hint, Warning, or Error",
     " * 'language': the language to validate with. If unspecified, this defaults to the language of the resource, then to english. This has the same syntax and semantics as the Accept-Language header",
@@ -11663,6 +11664,15 @@
       "module": "profile",
       "java": "java/R4.bundle-resolve-deep.json"
     },
+    {
+      "name": "identifier-systems",
+      "file": "patient-identifiers.xml",
+      "description": "Check that identifier systems are valid",
+      "version": "4.0",
+      "module": "(default)",
+      "strictIdentifierSystems": true,
+      "java": "java/R4.identifier-systems-base.json"
+    },
     {
       "name": "zzz",
       "file": "zzz.json",
diff --git a/validator/outcomes/java/R4.identifier-systems-base.json b/validator/outcomes/java/R4.identifier-systems-base.json
new file mode 100644
index 00000000..b11590e3
--- /dev/null
+++ b/validator/outcomes/java/R4.identifier-systems-base.json
@@ -0,0 +1,12 @@
+{
+  "resourceType": "OperationOutcome",
+  "issue" : [{
+    "severity" : "information",
+    "code" : "business-rule",
+    "details" : {
+      "text" : "Identifier.system is not based on example.org or example.com and is not a preferred URI of any identifier system NamingSystems.  Ensure that the Identifier.system value is a properly defined system value"
+    },
+    "diagnostics" : "[8,14]",
+    "expression" : ["Patient.identifier[0]"]
+  }]
+}
\ No newline at end of file
diff --git a/validator/patient-identifiers.xml b/validator/patient-identifiers.xml
new file mode 100644
index 00000000..23a3b9cf
--- /dev/null
+++ b/validator/patient-identifiers.xml
@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Patient xmlns="http://hl7.org/fhir">
+	<id value="exampleidentifiers"/>
+	<text>
+		<status value="generated"/>
+		<div xmlns="http://www.w3.org/1999/xhtml">N/A</div>
+	</text>
+	<identifier>
+    <!-- This is unrecognized and should trigger a message -->
+		<system value="urn:oid:1.2.36.146.595.217.0.1"/>
+		<value value="Unrecognized"/>
+	</identifier>
+	<identifier>
+    <!-- This is an example system -->
+		<system value="http://example.org/someIdentifier"/>
+		<value value="thisisfine"/>
+	</identifier>
+	<identifier>
+    <!-- This is a registered system -->
+		<system value="http://hl7.org/fhir/sid/us-ssn"/>
+		<value value="123456789"/>
+	</identifier>
+	<active value="true"/>
+</Patient>
\ No newline at end of file