public void addNamespaceDeclaration(Namespace additionalNamespace) {
    if (additionalNamespaces == null) {
      additionalNamespaces = new ArrayList<>();
    }
    else {
      for (Namespace ns : additionalNamespaces) {
        if (ns == additionalNamespace) {
          return;
        }
      }
    }

    // Verify the new namespace prefix doesn't collide with another
    // declared namespace, an attribute prefix, or this element's prefix
    final String reason = Verifier.checkNamespaceCollision(additionalNamespace, this);
    if (reason != null) {
      throw new IllegalAddException(this, additionalNamespace, reason);
    }

    additionalNamespaces.add(additionalNamespace);
  }
public void addNamespaceDeclaration(Namespace additionalNamespace)