diff --git a/src/nu/validator/htmlparser/impl/AttributeName.java b/src/nu/validator/htmlparser/impl/AttributeName.java
index 35dc0231..6578915e 100644
--- a/src/nu/validator/htmlparser/impl/AttributeName.java
+++ b/src/nu/validator/htmlparser/impl/AttributeName.java
@@ -806,6 +806,7 @@ boolean equalsAnother(AttributeName another) {
     public static final AttributeName SRCDOC = new AttributeName(ALL_NO_NS, "srcdoc", "srcdoc", "srcdoc", "srcdoc", ALL_NO_PREFIX, NCNAME_HTML | NCNAME_FOREIGN | NCNAME_LANG);
     public static final AttributeName STDDEVIATION = new AttributeName(ALL_NO_NS, "stddeviation", "stddeviation", "stdDeviation", "stddeviation", ALL_NO_PREFIX, NCNAME_HTML | NCNAME_FOREIGN | NCNAME_LANG);
     public static final AttributeName SANDBOX = new AttributeName(ALL_NO_NS, "sandbox", "sandbox", "sandbox", "sandbox", ALL_NO_PREFIX, NCNAME_HTML | NCNAME_FOREIGN | NCNAME_LANG);
+    public static final AttributeName SHADOWROOTCUSTOMELEMENTREGISTRY = new AttributeName(ALL_NO_NS, "shadowrootcustomelementregistry", "shadowrootcustomelementregistry", "shadowrootcustomelementregistry", "shadowrootcustomelementregistry", ALL_NO_PREFIX, NCNAME_HTML | NCNAME_FOREIGN | NCNAME_LANG);
     public static final AttributeName SHADOWROOTDELEGATESFOCUS = new AttributeName(ALL_NO_NS, "shadowrootdelegatesfocus", "shadowrootdelegatesfocus", "shadowrootdelegatesfocus", "shadowrootdelegatesfocus", ALL_NO_PREFIX, NCNAME_HTML | NCNAME_FOREIGN | NCNAME_LANG);
     public static final AttributeName WORD_SPACING = new AttributeName(ALL_NO_NS, "word-spacing", "word-spacing", "word-spacing", "word-spacing", ALL_NO_PREFIX, NCNAME_HTML | NCNAME_FOREIGN | NCNAME_LANG);
     public static final AttributeName ACCENTUNDER = new AttributeName(ALL_NO_NS, "accentunder", "accentunder", "accentunder", "accentunder", ALL_NO_PREFIX, NCNAME_HTML | NCNAME_FOREIGN | NCNAME_LANG);
@@ -1512,6 +1513,7 @@ boolean equalsAnother(AttributeName another) {
     SHADOWROOTREFERENCETARGET,
     SHADOWROOTSERIALIZABLE,
     STDDEVIATION,
+    SHADOWROOTCUSTOMELEMENTREGISTRY,
     SHADOWROOTDELEGATESFOCUS,
     ACCENTUNDER,
     ACCESSKEY,
diff --git a/src/nu/validator/htmlparser/impl/TreeBuilder.java b/src/nu/validator/htmlparser/impl/TreeBuilder.java
index 3d4b3499..2bb1e711 100644
--- a/src/nu/validator/htmlparser/impl/TreeBuilder.java
+++ b/src/nu/validator/htmlparser/impl/TreeBuilder.java
@@ -2996,9 +2996,10 @@ private T getDeclarativeShadowRoot(T currentNode, T templateNode, HtmlAttributes
         boolean shadowRootIsClonable = attributes.contains(AttributeName.SHADOWROOTCLONABLE);
         boolean shadowRootIsSerializable = attributes.contains(AttributeName.SHADOWROOTSERIALIZABLE);
         boolean shadowRootDelegatesFocus = attributes.contains(AttributeName.SHADOWROOTDELEGATESFOCUS);
+        boolean shadowRootCustomElementRegistry = attributes.contains(AttributeName.SHADOWROOTCUSTOMELEMENTREGISTRY);
         String shadowRootReferenceTarget = attributes.getValue(AttributeName.SHADOWROOTREFERENCETARGET);
 
-        return getShadowRootFromHost(currentNode, templateNode, shadowRootMode, shadowRootIsClonable, shadowRootIsSerializable, shadowRootDelegatesFocus, shadowRootReferenceTarget);
+        return getShadowRootFromHost(currentNode, templateNode, shadowRootMode, shadowRootIsClonable, shadowRootIsSerializable, shadowRootDelegatesFocus, shadowRootCustomElementRegistry, shadowRootReferenceTarget);
     }
 
     /**
@@ -5379,7 +5380,7 @@ void setDocumentFragmentForTemplate(T template, T fragment) {
 
     T getShadowRootFromHost(T host, T template, String shadowRootMode,
             boolean shadowRootIsClonable, boolean shadowRootIsSerializable, boolean shadowRootDelegatesFocus,
-            String shadowRootReferenceTarget) {
+            boolean shadowRootCustomElementRegistry, String shadowRootReferenceTarget) {
         return null;
     }