diff --git a/pmd-ui/pom.xml b/pmd-ui/pom.xml
index c1a331ca7e..cc5829dbb8 100644
--- a/pmd-ui/pom.xml
+++ b/pmd-ui/pom.xml
@@ -36,5 +36,10 @@
             <artifactId>pmd-apex</artifactId>
             <version>6.0.0-SNAPSHOT</version>
         </dependency>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 </project>
diff --git a/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/DesignerWindowPresenter.java b/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/DesignerWindowPresenter.java
index 7c13d9b89e..2759736edc 100644
--- a/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/DesignerWindowPresenter.java
+++ b/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/DesignerWindowPresenter.java
@@ -44,7 +44,7 @@ import javafx.scene.control.TreeItem;
 import javafx.scene.control.TreeView;
 
 /**
- * Presenter of the designer window.
+ * Presenter of the designer window. Subscribes to the events of the {@link DesignerWindow} that instantiates it.
  *
  * @author Clément Fournier
  * @since 6.0.0
@@ -280,7 +280,7 @@ public class DesignerWindowPresenter {
         XMLSettingsSaver saver = XMLSettingsSaver.forFile(SETTINGS_FILE_NAME);
 
         for (DesignerWindowSettings setting : DesignerWindowSettings.values()) {
-            saver.put(setting.keyName, setting.getValueFrom(this));
+            saver.put(setting.getKeyName(), setting.getValueFrom(this));
         }
 
         saver.save();
@@ -291,7 +291,7 @@ public class DesignerWindowPresenter {
     private void loadSettings() throws IOException {
 
         Set<String> keyNames = Arrays.stream(DesignerWindowSettings.values())
-                                     .map(e -> e.keyName)
+                                     .map(DesignerWindowSettings::getKeyName)
                                      .collect(Collectors.toSet());
 
         XMLSettingsLoader loader = new XMLSettingsLoader(SETTINGS_FILE_NAME, keyNames);
@@ -304,8 +304,6 @@ public class DesignerWindowPresenter {
 
     /********************************/
     /* SETTINGS LOAD/STORE ROUTINES */
-
-
     /********************************/
 
 
diff --git a/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/DesignerWindowSettings.java b/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/DesignerWindowSettings.java
index 0239118700..b59c71459d 100644
--- a/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/DesignerWindowSettings.java
+++ b/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/DesignerWindowSettings.java
@@ -47,7 +47,7 @@ enum DesignerWindowSettings {
                                   DesignerWindowPresenter::setLeftToolbarDividerPosition);
 
 
-    public final String keyName;
+    private final String keyName;
     private final Function<DesignerWindowPresenter, String> getValueFunction;
     private final PresenterSettingSetter setValueFunction;
 
@@ -83,6 +83,11 @@ enum DesignerWindowSettings {
     }
 
 
+    public String getKeyName() {
+        return keyName;
+    }
+
+
     /** Get the setting from the name of its key. */
     static DesignerWindowSettings ofKeyName(String key) {
         return Arrays.stream(DesignerWindowSettings.values())
diff --git a/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/model/ASTManager.java b/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/model/ASTManager.java
index 2b73b80b99..9306e9af69 100644
--- a/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/model/ASTManager.java
+++ b/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/model/ASTManager.java
@@ -20,7 +20,7 @@ import javafx.collections.FXCollections;
 import javafx.collections.ObservableList;
 
 /**
- * Main class of the model.
+ * Main class of the model. Manages the compilation unit and evaluation logic.
  *
  * @author Clément Fournier
  * @since 6.0.0
@@ -61,7 +61,7 @@ public class ASTManager {
 
 
     public String getXPathVersion() {
-        return xpathEvaluator.xpathVersionProperty().get();
+        return xpathEvaluator.getXpathVersion();
     }
 
 
@@ -82,11 +82,11 @@ public class ASTManager {
 
 
     /**
-     * Evaluates an XPath request, returns the matching nodes.
+     * Evaluates an XPath query, returns the matching nodes.
      *
      * @param xpathQuery Query to execute
      *
-     * @return The matching nodes, or Optional.empty if the compilation unit is invalid.
+     * @return List of the matching nodes, never null.
      *
      * @throws XPathEvaluationException if there was an error during the evaluation. The cause is preserved.
      */
@@ -97,6 +97,13 @@ public class ASTManager {
     }
 
 
+    /**
+     * Returns true if the source must be recompiled.
+     *
+     * @param source Source to test
+     *
+     * @return true if the current AST does not correspond to the parameter source
+     */
     public boolean isRecompilationNeeded(String source) {
         return !StringUtils.equals(source, lastValidSource)
             || !languageVersion.get().equals(lastLanguageVersion);
diff --git a/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/model/XPathEvaluator.java b/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/model/XPathEvaluator.java
index 0e35689ce9..24312cbf80 100644
--- a/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/model/XPathEvaluator.java
+++ b/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/model/XPathEvaluator.java
@@ -33,7 +33,7 @@ class XPathEvaluator {
     private final StringProperty xpathVersion = new SimpleStringProperty();
 
 
-    public String getXpathVersion() {
+    String getXpathVersion() {
         return xpathVersion.get();
     }
 
diff --git a/pmd-ui/src/test/java/net/sourceforge/pmd/util/fxdesigner/DesignerWindowSettingsTest.java b/pmd-ui/src/test/java/net/sourceforge/pmd/util/fxdesigner/DesignerWindowSettingsTest.java
new file mode 100644
index 0000000000..e28233e485
--- /dev/null
+++ b/pmd-ui/src/test/java/net/sourceforge/pmd/util/fxdesigner/DesignerWindowSettingsTest.java
@@ -0,0 +1,28 @@
+package net.sourceforge.pmd.util.fxdesigner;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.junit.Test;
+
+/**
+ * @author Clément Fournier
+ * @since 6.0.0
+ */
+public class DesignerWindowSettingsTest {
+
+    @Test
+    public void testKeysNamesAreUnique() {
+        List<String> keyNames = Arrays.stream(DesignerWindowSettings.values())
+                                      .map(DesignerWindowSettings::getKeyName)
+                                      .collect(Collectors.toList());
+
+        assertEquals(keyNames.size(), new HashSet<>(keyNames).size());
+
+    }
+
+}
\ No newline at end of file