diff --git a/contributed_definitions/NXellipsometry.nxdl.xml b/contributed_definitions/NXellipsometry.nxdl.xml
index 5769036aff..eb4f483026 100644
--- a/contributed_definitions/NXellipsometry.nxdl.xml
+++ b/contributed_definitions/NXellipsometry.nxdl.xml
@@ -123,7 +123,7 @@ TODO (Workshop output):
                      definition was used for this entry/data.
                 </doc>
             </attribute>
-            <attribute name="URL">
+            <attribute name="URL" recommended="true">
                 <doc>
                      URL where to find further material (documentation, examples) relevant
                      to the application definition.
diff --git a/contributed_definitions/NXoptical_spectroscopy.nxdl.xml b/contributed_definitions/NXoptical_spectroscopy.nxdl.xml
index 61bd639a36..f70f9c16fc 100644
--- a/contributed_definitions/NXoptical_spectroscopy.nxdl.xml
+++ b/contributed_definitions/NXoptical_spectroscopy.nxdl.xml
@@ -81,7 +81,7 @@ TODO:
                      definition was used for this entry/data.
                 </doc>
             </attribute>
-            <attribute name="URL">
+            <attribute name="URL" recommended="true">
                 <doc>
                      URL where to find further material (documentation, examples) relevant
                      to the application definition.
@@ -311,7 +311,7 @@ TODO:
                 </field>
             </group>
             <group name="detector_TYPE" type="NXdetector" minOccurs="1" maxOccurs="unbounded">
-                <field name="detector_channel_type">
+                <field name="detector_channel_type" recommended="true">
                     <enumeration>
                         <item value="single-channel"/>
                         <item value="multichannel"/>
diff --git a/contributed_definitions/NXraman.nxdl.xml b/contributed_definitions/NXraman.nxdl.xml
index 02290711de..2a64eaf8e1 100644
--- a/contributed_definitions/NXraman.nxdl.xml
+++ b/contributed_definitions/NXraman.nxdl.xml
@@ -159,7 +159,7 @@ dataset examples (i.e. NXdata_raman)-->
                      definition was used for this entry/data.
                 </doc>
             </attribute>
-            <attribute name="URL">
+            <attribute name="URL" recommended="true">
                 <doc>
                      URL where to find further material (documentation, examples) relevant
                      to the application definition.
diff --git a/contributed_definitions/nyaml/NXellipsometry.yaml b/contributed_definitions/nyaml/NXellipsometry.yaml
index 7d95cdcdbe..7dc955ccfc 100644
--- a/contributed_definitions/nyaml/NXellipsometry.yaml
+++ b/contributed_definitions/nyaml/NXellipsometry.yaml
@@ -87,6 +87,7 @@ NXellipsometry(NXoptical_spectroscopy):
           Version number to identify which definition of this application
           definition was used for this entry/data.
       \@URL:
+        exists: recommended
         doc: |
           URL where to find further material (documentation, examples) relevant
           to the application definition.
diff --git a/contributed_definitions/nyaml/NXoptical_spectroscopy.yaml b/contributed_definitions/nyaml/NXoptical_spectroscopy.yaml
index 19dc970a83..0359eeaa76 100644
--- a/contributed_definitions/nyaml/NXoptical_spectroscopy.yaml
+++ b/contributed_definitions/nyaml/NXoptical_spectroscopy.yaml
@@ -49,6 +49,7 @@ NXoptical_spectroscopy(NXobject):
           Version number to identify which definition of this application
           definition was used for this entry/data.
       \@URL:
+        exists: recommended
         doc: |
           URL where to find further material (documentation, examples) relevant
           to the application definition.
@@ -239,6 +240,7 @@ NXoptical_spectroscopy(NXobject):
       detector_TYPE(NXdetector):
         exists: ['min', '1', 'max', 'unbounded']
         detector_channel_type:
+          exists: recommended
           enumeration: [single-channel, multichannel]
         detector_type:
           exists: recommended
diff --git a/contributed_definitions/nyaml/NXraman.yaml b/contributed_definitions/nyaml/NXraman.yaml
index 77d36c5c5d..fe4fae54d4 100644
--- a/contributed_definitions/nyaml/NXraman.yaml
+++ b/contributed_definitions/nyaml/NXraman.yaml
@@ -117,6 +117,7 @@ NXraman(NXoptical_spectroscopy):
           Version number to identify which definition of this application
           definition was used for this entry/data.
       \@URL:
+        exists: recommended
         doc: |
           URL where to find further material (documentation, examples) relevant
           to the application definition.
diff --git a/requirements.txt b/requirements.txt
index 74294d9b26..d1830c7238 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,7 +1,7 @@
 # Prepare for Documentation
 lxml>=4.9.1 
 pyyaml
-nyaml==0.0.8
+nyaml==0.1.2
 
 # Documentation building
 sphinx>=5