diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index 25e6bf73ba..b14fba2cd1 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -850,6 +850,7 @@ CPU Tuning
    to which vCPUs this allocation applies. A vCPU can only be member of one
    ``cachetune`` element allocation. The vCPUs specified by cachetune can be
    identical with those in memorytune, however they are not allowed to overlap.
+   The optional, output only ``id`` attribute identifies cache uniquely.
    Supported subelements are:
 
    ``cache``
diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index 5ea14b6dbf..c6643bbc7f 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -1006,6 +1006,11 @@
             <attribute name="vcpus">
               <ref name="cpuset"/>
             </attribute>
+            <optional>
+              <attribute name="id">
+                <data type="string"/>
+              </attribute>
+            </optional>
             <oneOrMore>
               <choice>
                 <element name="cache">