diff --git a/src/main/java/org/xembly/Output.java b/src/main/java/org/xembly/Output.java
index b13a449..025fa89 100644
--- a/src/main/java/org/xembly/Output.java
+++ b/src/main/java/org/xembly/Output.java
@@ -1,3 +1,32 @@
+/*
+ * Copyright (c) 2013-2023, xembly.org
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met: 1) Redistributions of source code must retain the above
+ * copyright notice, this list of conditions and the following
+ * disclaimer. 2) Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following
+ * disclaimer in the documentation and/or other materials provided
+ * with the distribution. 3) Neither the name of the xembly.org nor
+ * the names of its contributors may be used to endorse or promote
+ * products derived from this software without specific prior written
+ * permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT
+ * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
 package org.xembly;
 
 import java.util.HashMap;
@@ -5,30 +34,61 @@
 import javax.xml.transform.OutputKeys;
 import javax.xml.transform.Transformer;
 
+/**
+ * Output type for Xembler to use.
+ * Allows to configure the output.
+ * @since 0.30
+ */
 public interface Output {
 
 
-    void prepareTransformer(final Transformer transformer);
-
+    /**
+     * Prepare transformer before using it.
+     * @param transformer Transformer to prepare.
+     * @since 0.30
+     */
+    void prepare(final Transformer transformer);
 
+    /**
+     * Document output.
+     * Can accept properties to configure the output.
+     * @since 0.30
+     */
     final class Document implements Output {
 
+        /**
+         * Properties to configure the output.
+         */
         private final Map<String, String> properties;
 
+        /**
+         * Ctor.
+         * Uses default properties.
+         * @since 0.30
+         */
         public Document() {
             this((Document.defaultProperties()));
         }
 
+        /**
+         * Ctor.
+         * @param properties Properties to configure the output.
+         * @since 0.30
+         */
         public Document(final Map<String, String> properties) {
             this.properties = properties;
         }
 
         @Override
-        public void prepareTransformer(final Transformer transformer) {
+        public void prepare(final Transformer transformer) {
             this.properties.entrySet().stream()
                 .forEach((e) -> transformer.setOutputProperty(e.getKey(), e.getValue()));
         }
 
+        /**
+         * Default properties prestructor.
+         * @return Properties to configure the output.
+         */
         private static Map<String, String> defaultProperties() {
             final HashMap<String, String> res = new HashMap<>();
             res.put(OutputKeys.INDENT, "yes");
@@ -37,10 +97,15 @@ private static Map<String, String> defaultProperties() {
         }
     }
 
+    /**
+     * Node output.
+     * Omits XML declaration: <?xml version="1.0" encoding="UTF-8"?>
+     * @since 0.30
+     */
     final class Node implements Output {
 
         @Override
-        public void prepareTransformer(final Transformer transformer) {
+        public void prepare(final Transformer transformer) {
             transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
         }
     }
diff --git a/src/main/java/org/xembly/Xembler.java b/src/main/java/org/xembly/Xembler.java
index 21f4081..ff9f47f 100644
--- a/src/main/java/org/xembly/Xembler.java
+++ b/src/main/java/org/xembly/Xembler.java
@@ -33,7 +33,6 @@
 import java.util.Collections;
 import javax.xml.parsers.DocumentBuilderFactory;
 import javax.xml.parsers.ParserConfigurationException;
-import javax.xml.transform.OutputKeys;
 import javax.xml.transform.Transformer;
 import javax.xml.transform.TransformerConfigurationException;
 import javax.xml.transform.TransformerException;
@@ -259,7 +258,7 @@ public String xml() throws ImpossibleModificationException {
                 ex
             );
         }
-        this.output.prepareTransformer(transformer);
+        this.output.prepare(transformer);
 //        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
 //        transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
         final StringWriter writer = new StringWriter();