diff --git a/docs/pages/release_notes.md b/docs/pages/release_notes.md
index 24e69a593f..5afda090bc 100644
--- a/docs/pages/release_notes.md
+++ b/docs/pages/release_notes.md
@@ -393,6 +393,10 @@ package or made (package) private and are _not accessible_ anymore.
     * Method `replacementIfDeprecated()` is now package private.
   * `net.sourceforge.pmd.properties.PropertyTypeId` - moved in subpackage `internal`.
   * {%jdoc !!core::properties.PropertyDescriptor %} - method `getTypeId()` is now package private.
+* pmd-doc
+  * The whole maven module `pmd-doc` is now considered internal API even though it was not declared so before.
+    It's used to generate the rule documentation for the built-in rules.
+  * All the classes have been moved into package `net.sourceforge.pmd.doc.internal`.
 * pmd-ant
   * {%jdoc !!ant::ant.Formatter %}
     * Method `getRenderer()` has been removed.
diff --git a/pmd-doc/pom.xml b/pmd-doc/pom.xml
index 55529bfed2..e449a52d79 100644
--- a/pmd-doc/pom.xml
+++ b/pmd-doc/pom.xml
@@ -2,7 +2,7 @@
 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>
     <artifactId>pmd-doc</artifactId>
-    <name>PMD Documentation Generator</name>
+    <name>PMD Documentation Generator (internal)</name>
     <packaging>jar</packaging>
 
     <parent>
@@ -35,7 +35,7 @@
                                 </goals>
                                 <phase>package</phase>
                                 <configuration>
-                                    <mainClass>net.sourceforge.pmd.docs.GenerateRuleDocsCmd</mainClass>
+                                    <mainClass>net.sourceforge.pmd.doc.internal.GenerateRuleDocsCmd</mainClass>
                                     <arguments>
                                         <argument>${project.basedir}</argument>
                                     </arguments>
@@ -48,7 +48,7 @@
                                 </goals>
                                 <phase>verify</phase>
                                 <configuration>
-                                    <mainClass>net.sourceforge.pmd.docs.DeadLinksChecker</mainClass>
+                                    <mainClass>net.sourceforge.pmd.doc.internal.DeadLinksChecker</mainClass>
                                     <arguments>
                                         <argument>${project.basedir}</argument>
                                     </arguments>
@@ -61,7 +61,7 @@
                                 </goals>
                                 <phase>verify</phase>
                                 <configuration>
-                                    <mainClass>net.sourceforge.pmd.docs.RuleTagChecker</mainClass>
+                                    <mainClass>net.sourceforge.pmd.doc.internal.RuleTagChecker</mainClass>
                                     <arguments>
                                         <argument>${project.basedir}</argument>
                                     </arguments>
diff --git a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/DeadLinksChecker.java b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/DeadLinksChecker.java
similarity index 99%
rename from pmd-doc/src/main/java/net/sourceforge/pmd/docs/DeadLinksChecker.java
rename to pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/DeadLinksChecker.java
index 9e3b11c5c2..ad849464da 100644
--- a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/DeadLinksChecker.java
+++ b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/DeadLinksChecker.java
@@ -2,7 +2,7 @@
  * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
  */
 
-package net.sourceforge.pmd.docs;
+package net.sourceforge.pmd.doc.internal;
 
 import java.io.IOException;
 import java.io.InputStream;
diff --git a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/DefaultFileWriter.java b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/DefaultFileWriter.java
similarity index 92%
rename from pmd-doc/src/main/java/net/sourceforge/pmd/docs/DefaultFileWriter.java
rename to pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/DefaultFileWriter.java
index 5c7e84ad2f..3a105f05d2 100644
--- a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/DefaultFileWriter.java
+++ b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/DefaultFileWriter.java
@@ -2,7 +2,7 @@
  * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
  */
 
-package net.sourceforge.pmd.docs;
+package net.sourceforge.pmd.doc.internal;
 
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
diff --git a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/EscapeUtils.java b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/EscapeUtils.java
similarity index 98%
rename from pmd-doc/src/main/java/net/sourceforge/pmd/docs/EscapeUtils.java
rename to pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/EscapeUtils.java
index 78e5a4fd57..1dda3b8182 100644
--- a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/EscapeUtils.java
+++ b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/EscapeUtils.java
@@ -2,7 +2,7 @@
  * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
  */
 
-package net.sourceforge.pmd.docs;
+package net.sourceforge.pmd.doc.internal;
 
 import java.util.List;
 import java.util.regex.Matcher;
diff --git a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/FileWriter.java b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/FileWriter.java
similarity index 86%
rename from pmd-doc/src/main/java/net/sourceforge/pmd/docs/FileWriter.java
rename to pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/FileWriter.java
index d47452754d..e00b335f02 100644
--- a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/FileWriter.java
+++ b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/FileWriter.java
@@ -2,7 +2,7 @@
  * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
  */
 
-package net.sourceforge.pmd.docs;
+package net.sourceforge.pmd.doc.internal;
 
 import java.io.IOException;
 import java.nio.file.Path;
diff --git a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/GenerateRuleDocsCmd.java b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/GenerateRuleDocsCmd.java
similarity index 98%
rename from pmd-doc/src/main/java/net/sourceforge/pmd/docs/GenerateRuleDocsCmd.java
rename to pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/GenerateRuleDocsCmd.java
index 256e605904..c1958e9c39 100644
--- a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/GenerateRuleDocsCmd.java
+++ b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/GenerateRuleDocsCmd.java
@@ -2,7 +2,7 @@
  * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
  */
 
-package net.sourceforge.pmd.docs;
+package net.sourceforge.pmd.doc.internal;
 
 import java.io.File;
 import java.io.IOException;
diff --git a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/RuleDocGenerator.java b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/RuleDocGenerator.java
similarity index 99%
rename from pmd-doc/src/main/java/net/sourceforge/pmd/docs/RuleDocGenerator.java
rename to pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/RuleDocGenerator.java
index a5d32cc979..cdaec8328e 100644
--- a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/RuleDocGenerator.java
+++ b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/RuleDocGenerator.java
@@ -2,7 +2,7 @@
  * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
  */
 
-package net.sourceforge.pmd.docs;
+package net.sourceforge.pmd.doc.internal;
 
 import java.io.File;
 import java.io.IOException;
diff --git a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/RuleSetUtils.java b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/RuleSetUtils.java
similarity index 98%
rename from pmd-doc/src/main/java/net/sourceforge/pmd/docs/RuleSetUtils.java
rename to pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/RuleSetUtils.java
index 156946cfbc..2399f96ebd 100644
--- a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/RuleSetUtils.java
+++ b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/RuleSetUtils.java
@@ -2,7 +2,7 @@
  * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
  */
 
-package net.sourceforge.pmd.docs;
+package net.sourceforge.pmd.doc.internal;
 
 import java.io.File;
 import java.util.regex.Pattern;
diff --git a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/RuleTagChecker.java b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/RuleTagChecker.java
similarity index 99%
rename from pmd-doc/src/main/java/net/sourceforge/pmd/docs/RuleTagChecker.java
rename to pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/RuleTagChecker.java
index a1ae35b753..9e41a1fa32 100644
--- a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/RuleTagChecker.java
+++ b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/RuleTagChecker.java
@@ -2,7 +2,7 @@
  * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
  */
 
-package net.sourceforge.pmd.docs;
+package net.sourceforge.pmd.doc.internal;
 
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
diff --git a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/SidebarGenerator.java b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/SidebarGenerator.java
similarity index 99%
rename from pmd-doc/src/main/java/net/sourceforge/pmd/docs/SidebarGenerator.java
rename to pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/SidebarGenerator.java
index 0982f7fb5b..d9f248eb0c 100644
--- a/pmd-doc/src/main/java/net/sourceforge/pmd/docs/SidebarGenerator.java
+++ b/pmd-doc/src/main/java/net/sourceforge/pmd/doc/internal/SidebarGenerator.java
@@ -2,7 +2,7 @@
  * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
  */
 
-package net.sourceforge.pmd.docs;
+package net.sourceforge.pmd.doc.internal;
 
 import java.io.IOException;
 import java.io.Reader;
diff --git a/pmd-doc/src/test/java/net/sourceforge/pmd/docs/EscapeUtilsTest.java b/pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/EscapeUtilsTest.java
similarity index 98%
rename from pmd-doc/src/test/java/net/sourceforge/pmd/docs/EscapeUtilsTest.java
rename to pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/EscapeUtilsTest.java
index 439a9f41bc..fe83327d77 100644
--- a/pmd-doc/src/test/java/net/sourceforge/pmd/docs/EscapeUtilsTest.java
+++ b/pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/EscapeUtilsTest.java
@@ -2,7 +2,7 @@
  * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
  */
 
-package net.sourceforge.pmd.docs;
+package net.sourceforge.pmd.doc.internal;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
diff --git a/pmd-doc/src/test/java/net/sourceforge/pmd/docs/MockedFileWriter.java b/pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/MockedFileWriter.java
similarity index 96%
rename from pmd-doc/src/test/java/net/sourceforge/pmd/docs/MockedFileWriter.java
rename to pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/MockedFileWriter.java
index b954a3a9d3..7173fcc927 100644
--- a/pmd-doc/src/test/java/net/sourceforge/pmd/docs/MockedFileWriter.java
+++ b/pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/MockedFileWriter.java
@@ -2,7 +2,7 @@
  * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
  */
 
-package net.sourceforge.pmd.docs;
+package net.sourceforge.pmd.doc.internal;
 
 import java.io.IOException;
 import java.nio.file.Path;
diff --git a/pmd-doc/src/test/java/net/sourceforge/pmd/docs/RuleDocGeneratorTest.java b/pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/RuleDocGeneratorTest.java
similarity index 96%
rename from pmd-doc/src/test/java/net/sourceforge/pmd/docs/RuleDocGeneratorTest.java
rename to pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/RuleDocGeneratorTest.java
index b593280141..cffe8af125 100644
--- a/pmd-doc/src/test/java/net/sourceforge/pmd/docs/RuleDocGeneratorTest.java
+++ b/pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/RuleDocGeneratorTest.java
@@ -2,7 +2,7 @@
  * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
  */
 
-package net.sourceforge.pmd.docs;
+package net.sourceforge.pmd.doc.internal;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -19,7 +19,7 @@ import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
 
-import net.sourceforge.pmd.docs.MockedFileWriter.FileEntry;
+import net.sourceforge.pmd.doc.internal.MockedFileWriter.FileEntry;
 import net.sourceforge.pmd.internal.util.IOUtil;
 import net.sourceforge.pmd.lang.rule.RuleSet;
 import net.sourceforge.pmd.lang.rule.RuleSetLoader;
diff --git a/pmd-doc/src/test/java/net/sourceforge/pmd/docs/RuleSetResolverTest.java b/pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/RuleSetResolverTest.java
similarity index 98%
rename from pmd-doc/src/test/java/net/sourceforge/pmd/docs/RuleSetResolverTest.java
rename to pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/RuleSetResolverTest.java
index bd3ee01d54..9abb6b4618 100644
--- a/pmd-doc/src/test/java/net/sourceforge/pmd/docs/RuleSetResolverTest.java
+++ b/pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/RuleSetResolverTest.java
@@ -2,7 +2,7 @@
  * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
  */
 
-package net.sourceforge.pmd.docs;
+package net.sourceforge.pmd.doc.internal;
 
 import static net.sourceforge.pmd.util.CollectionUtil.listOf;
 import static org.junit.jupiter.api.Assertions.assertFalse;
diff --git a/pmd-doc/src/test/java/net/sourceforge/pmd/docs/RuleTagCheckerTest.java b/pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/RuleTagCheckerTest.java
similarity index 97%
rename from pmd-doc/src/test/java/net/sourceforge/pmd/docs/RuleTagCheckerTest.java
rename to pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/RuleTagCheckerTest.java
index 3808b616a5..d9aa3cf7a1 100644
--- a/pmd-doc/src/test/java/net/sourceforge/pmd/docs/RuleTagCheckerTest.java
+++ b/pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/RuleTagCheckerTest.java
@@ -3,7 +3,7 @@
  */
 
 
-package net.sourceforge.pmd.docs;
+package net.sourceforge.pmd.doc.internal;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
diff --git a/pmd-doc/src/test/java/net/sourceforge/pmd/docs/SidebarGeneratorTest.java b/pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/SidebarGeneratorTest.java
similarity index 98%
rename from pmd-doc/src/test/java/net/sourceforge/pmd/docs/SidebarGeneratorTest.java
rename to pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/SidebarGeneratorTest.java
index 68ce308d5b..81f3392583 100644
--- a/pmd-doc/src/test/java/net/sourceforge/pmd/docs/SidebarGeneratorTest.java
+++ b/pmd-doc/src/test/java/net/sourceforge/pmd/doc/internal/SidebarGeneratorTest.java
@@ -2,7 +2,7 @@
  * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
  */
 
-package net.sourceforge.pmd.docs;
+package net.sourceforge.pmd.doc.internal;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
diff --git a/pmd-doc/src/test/resources/net/sourceforge/pmd/docs/sidebar.yml b/pmd-doc/src/test/resources/net/sourceforge/pmd/doc/internal/sidebar.yml
similarity index 100%
rename from pmd-doc/src/test/resources/net/sourceforge/pmd/docs/sidebar.yml
rename to pmd-doc/src/test/resources/net/sourceforge/pmd/doc/internal/sidebar.yml