diff --git a/docs/schemas/secret.rng b/docs/schemas/secret.rng
index 2aab1db1f8..40e2b7ffa6 100644
--- a/docs/schemas/secret.rng
+++ b/docs/schemas/secret.rng
@@ -7,40 +7,40 @@
   <define name='secret'>
     <element name='secret'>
       <optional>
-	<attribute name='ephemeral'>
-	  <choice>
-	    <value>yes</value>
-	    <value>no</value>
-	  </choice>
-	</attribute>
+        <attribute name='ephemeral'>
+          <choice>
+            <value>yes</value>
+            <value>no</value>
+          </choice>
+        </attribute>
       </optional>
       <optional>
-	<attribute name='private'>
-	  <choice>
-	    <value>yes</value>
-	    <value>no</value>
-	  </choice>
-	</attribute>
+        <attribute name='private'>
+          <choice>
+            <value>yes</value>
+            <value>no</value>
+          </choice>
+        </attribute>
       </optional>
       <interleave>
-	<optional>
-	  <element name='uuid'>
-	    <ref name='UUID'/>
-	  </element>
-	</optional>
-	<optional>
-	  <element name='description'>
-	    <text/>
-	  </element>
-	</optional>
-	<optional>
-	  <element name='usage'>
-	    <choice>
-	      <ref name='usagevolume'>
-	    </choice>
-	    <text/>
-	  </element>
-	</optional>
+        <optional>
+          <element name='uuid'>
+            <ref name='UUID'/>
+          </element>
+        </optional>
+        <optional>
+          <element name='description'>
+            <text/>
+          </element>
+        </optional>
+        <optional>
+          <element name='usage'>
+            <choice>
+              <ref name='usagevolume'>
+              <!-- More choices later -->
+            </choice>
+          </element>
+        </optional>
       </interleave>
     </element>
   </define>
@@ -50,7 +50,7 @@
       <value>volume</value>
     </attribute>
     <element name='volume'>
-      <text/>
+      <ref name='absFilePath'/>
     </element>
   </define>
 
@@ -65,4 +65,10 @@
     </choice>
   </define>
 
+  <define name="absFilePath">
+    <data type="string">
+      <param name="pattern">/[a-zA-Z0-9_\.\+\-&amp;/%]+</param>
+    </data>
+  </define>
+
 </grammar>