diff -r 2f6f1d20fa7a json/src/main/java/net/java/html/json/Function.java
--- a/json/src/main/java/net/java/html/json/Function.java	Wed Dec 02 08:44:31 2015 +0100
+++ b/json/src/main/java/net/java/html/json/Function.java	Mon Dec 07 23:26:27 2015 +0100
@@ -52,7 +52,8 @@
 /** Methods in class annotated by {@link Model} can be 
  * annotated by this annotation to signal that they should be available
  * as functions to users of the model classes. The method
- * should be non-private, static and return <code>void</code>.
+ * should be non-private, static (unless {@link Model#instance() instance mode} is on)
+ * and return <code>void</code>.
  * It may take few arguments. The first argument can be the type of
  * the associated model class, the other argument can be of any type,
  * but has to be named <code>data</code> - this one represents the
diff -r 2f6f1d20fa7a json/src/main/java/net/java/html/json/Model.java
--- a/json/src/main/java/net/java/html/json/Model.java	Wed Dec 02 08:44:31 2015 +0100
+++ b/json/src/main/java/net/java/html/json/Model.java	Mon Dec 07 23:26:27 2015 +0100
@@ -247,4 +247,46 @@
      * @since 1.3
      */
     String builder() default "";
+    
+    /** Controls keeping of per-instance private state. Sometimes
+     * the class generated by the {@link Model @Model annotation} needs to
+     * keep non-public, or non-JSON like state. One can achieve that by
+     * specifying <code>instance=true</code> when using the annotation. Then
+     * the generated class gets a pointer to the instance of the annotated
+     * class (there needs to be default constructor) and all the {@link ModelOperation @ModelOperation},
+     * {@link Function @Function}, {@link OnPropertyChange @OnPropertyChange}
+     * and {@link OnReceive @OnReceive} methods may be non-static. The
+     * instance of the implementation class isn't accessible directly, just
+     * through calls to above defined (non-static) methods. Example:
+     * <pre>
+     * {@link Model @Model}(className="Data", instance=<b>true</b>, properties={
+     *   {@link Property @Property}(name="message", type=String.<b>class</b>)
+     * })
+     * <b>final class</b> DataPrivate {
+     *   <b>private int</b> count;
+     * 
+     *   {@link ModelOperation @ModelOperation} <b>void</b> increment(Data model) {
+     *     count++;
+     *   }
+     * 
+     *   {@link ModelOperation @ModelOperation} <b>void</b> hello(Data model) {
+     *     model.setMessage("Hello " + count + " times!");
+     *   }
+     * }
+     * Data data = <b>new</b> Data();
+     * data.increment();
+     * data.increment();
+     * data.increment();
+     * data.hello();
+     * <b>assert</b> data.getMessage().equals("Hello 3 times!");
+     * </pre>
+     * The methods annotated by {@link ComputedProperty} need to remain static, as 
+     * they are supposed to be <em>pure</em> functions (e.g. depend only on their parameters)
+     * and shouldn't use any internal state.
+     * 
+     * @return <code>true</code> if the model class should keep pointer to
+     *   instance of the implementation class
+     * @since 1.3
+     */
+    boolean instance() default false;
 }
diff -r 2f6f1d20fa7a json/src/main/java/net/java/html/json/ModelOperation.java
--- a/json/src/main/java/net/java/html/json/ModelOperation.java	Wed Dec 02 08:44:31 2015 +0100
+++ b/json/src/main/java/net/java/html/json/ModelOperation.java	Mon Dec 07 23:26:27 2015 +0100
@@ -53,7 +53,8 @@
  * <p>
  * A method in a class annotated by {@link Model @Model} annotation may be
  * annotated by {@link ModelOperation @ModelOperation}. The method has
- * to be static, non-private and return <code>void</code>. The first parameter
+ * to be static (unless {@link Model#instance() instance mode} is on), 
+ * non-private and return <code>void</code>. The first parameter
  * of the method must be the {@link Model#className() model class} followed
  * by any number of additional arguments.
  * <p>
diff -r 2f6f1d20fa7a json/src/main/java/net/java/html/json/OnPropertyChange.java
--- a/json/src/main/java/net/java/html/json/OnPropertyChange.java	Wed Dec 02 08:44:31 2015 +0100
+++ b/json/src/main/java/net/java/html/json/OnPropertyChange.java	Mon Dec 07 23:26:27 2015 +0100
@@ -74,7 +74,8 @@
  * }
  * </pre>
  * The method's first argument should be the instance of the 
- * associated {@link Model model class}.
+ * associated {@link Model model class}. The method shall be non-private
+ * and unless {@link Model#instance() instance mode} is on also static.
  * There can be an optional second {@link String} argument which will be set
  * to the name of the changed property. The second argument is only useful when
  * a single method reacts to changes in multiple properties.
diff -r 2f6f1d20fa7a json/src/main/java/net/java/html/json/OnReceive.java
--- a/json/src/main/java/net/java/html/json/OnReceive.java	Wed Dec 02 08:44:31 2015 +0100
+++ b/json/src/main/java/net/java/html/json/OnReceive.java	Mon Dec 07 23:26:27 2015 +0100
@@ -102,6 +102,8 @@
  * One can use this method to communicate with the server
  * via <a href="doc-files/websockets.html">WebSocket</a> protocol since version 0.6.
  * Read the <a href="doc-files/websockets.html">tutorial</a> to see how.
+ * The method shall be non-private
+ * and unless {@link Model#instance() instance mode} is on also static.
  * <p>
  * Visit an <a target="_blank" href="http://dew.apidesign.org/dew/#7138581">on-line demo</a>
  * to see REST access via {@link OnReceive} annotation.
diff -r 2f6f1d20fa7a json/src/main/java/org/netbeans/html/json/impl/ModelProcessor.java
--- a/json/src/main/java/org/netbeans/html/json/impl/ModelProcessor.java	Wed Dec 02 08:44:31 2015 +0100
+++ b/json/src/main/java/org/netbeans/html/json/impl/ModelProcessor.java	Mon Dec 07 23:26:27 2015 +0100
@@ -223,11 +223,36 @@
             try {
                 w.append("package " + pkg + ";\n");
                 w.append("import net.java.html.json.*;\n");
-                final String inPckName = inPckName(e);
+                final String inPckName = inPckName(e, false);
                 w.append("/** Generated for {@link ").append(inPckName).append("}*/\n");
                 w.append("public final class ").append(className).append(" implements Cloneable {\n");
                 w.append("  private static Class<").append(inPckName).append("> modelFor() { return ").append(inPckName).append(".class; }\n");
                 w.append("  private static final Html4JavaType TYPE = new Html4JavaType();\n");
+                if (m.instance()) {
+                    int cCnt = 0;
+                    for (Element c : e.getEnclosedElements()) {
+                        if (c.getKind() != ElementKind.CONSTRUCTOR) {
+                            continue;
+                        }
+                        cCnt++;
+                        ExecutableElement ec = (ExecutableElement) c;
+                        if (ec.getParameters().size() > 0) {
+                            continue;
+                        }
+                        if (ec.getModifiers().contains(Modifier.PRIVATE)) {
+                            continue;
+                        }
+                        cCnt = 0;
+                        break;
+                    }
+                    if (cCnt > 0) {
+                        ok = false;
+                        error("Needs non-private default constructor when instance=true", e);
+                        w.append("  private final ").append(inPckName).append(" instance = null;\n");
+                    } else {
+                        w.append("  private final ").append(inPckName).append(" instance = new ").append(inPckName).append("();\n");
+                    }
+                }
                 w.append("  private final org.netbeans.html.json.spi.Proto proto;\n");
                 w.append(body.toString());
                 w.append("  private ").append(className).append("(net.java.html.BrwsrCtx context) {\n");
@@ -382,7 +407,13 @@
                     if (param instanceof ExecutableElement) {
                         ExecutableElement ee = (ExecutableElement)param;
                         w.append("        case " + (i / 2) + ":\n");
-                        w.append("          ").append(((TypeElement)e).getQualifiedName()).append(".").append(name).append("(");
+                        w.append("          ");
+                        if (m.instance()) {
+                            w.append("model.instance");
+                        } else {
+                            w.append(((TypeElement)e).getQualifiedName());
+                        }
+                        w.append(".").append(name).append("(");
                         w.append(wrapParams(ee, null, className, "model", "ev", "data"));
                         w.append(");\n");
                         w.append("          return;\n");
@@ -939,6 +970,7 @@
         Element clazz, StringWriter body, String className,
         List<? extends Element> enclosedElements, List<Object> functions
     ) {
+        boolean instance = clazz.getAnnotation(Model.class).instance();
         for (Element m : enclosedElements) {
             if (m.getKind() != ElementKind.METHOD) {
                 continue;
@@ -948,7 +980,7 @@
             if (onF == null) {
                 continue;
             }
-            if (!e.getModifiers().contains(Modifier.STATIC)) {
+            if (!instance && !e.getModifiers().contains(Modifier.STATIC)) {
                 error("@OnFunction method needs to be static", e);
                 return false;
             }
@@ -971,6 +1003,7 @@
         Prprt[] properties, String className,
         Map<String, Collection<String>> functionDeps
     ) {
+        boolean instance = clazz.getAnnotation(Model.class).instance();
         for (Element m : clazz.getEnclosedElements()) {
             if (m.getKind() != ElementKind.METHOD) {
                 continue;
@@ -986,7 +1019,7 @@
                     return false;
                 }
             }
-            if (!e.getModifiers().contains(Modifier.STATIC)) {
+            if (!instance && !e.getModifiers().contains(Modifier.STATIC)) {
                 error("@OnPrprtChange method needs to be static", e);
                 return false;
             }
@@ -1003,7 +1036,7 @@
 
             for (String pn : onPC.value()) {
                 StringBuilder call = new StringBuilder();
-                call.append("  ").append(clazz.getSimpleName()).append(".").append(n).append("(");
+                call.append("  ").append(inPckName(clazz, instance)).append(".").append(n).append("(");
                 call.append(wrapPropName(e, className, "name", pn));
                 call.append(");\n");
 
@@ -1031,6 +1064,7 @@
         List<? extends Element> enclosedElements,
         List<Object> functions
     ) {
+        boolean instance = clazz.getAnnotation(Model.class).instance();
         for (Element m : enclosedElements) {
             if (m.getKind() != ElementKind.METHOD) {
                 continue;
@@ -1040,7 +1074,7 @@
             if (mO == null) {
                 continue;
             }
-            if (!e.getModifiers().contains(Modifier.STATIC)) {
+            if (!instance && !e.getModifiers().contains(Modifier.STATIC)) {
                 error("@ModelOperation method needs to be static", e);
                 return false;
             }
@@ -1091,7 +1125,7 @@
 
                 StringBuilder call = new StringBuilder();
                 call.append("{ Object[] arr = (Object[])data; ");
-                call.append(inPckName(clazz)).append(".").append(m.getSimpleName()).append("(");
+                call.append(inPckName(clazz, true)).append(".").append(m.getSimpleName()).append("(");
                 int i = 0;
                 for (VariableElement ve : e.getParameters()) {
                     if (i++ == 0) {
@@ -1132,6 +1166,7 @@
         inType.append("    switch (index) {\n");
         int index = 0;
         boolean ok = true;
+        boolean instance = clazz.getAnnotation(Model.class).instance();
         for (Element m : enclosedElements) {
             if (m.getKind() != ElementKind.METHOD) {
                 continue;
@@ -1141,7 +1176,7 @@
             if (onR == null) {
                 continue;
             }
-            if (!e.getModifiers().contains(Modifier.STATIC)) {
+            if (!instance && !e.getModifiers().contains(Modifier.STATIC)) {
                 error("@OnReceive method needs to be static", e);
                 return false;
             }
@@ -1391,7 +1426,7 @@
         body.append(
             "    case " + index + ": {\n" +
             "      if (type == 0) { /* on open */\n" +
-            "        ").append(inPckName(clazz)).append(".").append(n).append("(");
+            "        ").append(inPckName(clazz, true)).append(".").append(n).append("(");
         {
             String sep = "";
             for (String arg : args) {
@@ -1418,7 +1453,7 @@
             if (!findOnError(e, ((TypeElement)clazz), onR.onError(), className)) {
                 return true;
             }
-            body.append("        ").append(inPckName(clazz)).append(".").append(onR.onError()).append("(");
+            body.append("        ").append(inPckName(clazz, true)).append(".").append(onR.onError()).append("(");
             body.append("model, value);\n");
         }
         body.append(
@@ -1439,7 +1474,7 @@
             "        TYPE.copyJSON(model.proto.getContext(), ev, " + modelClass + ".class, arr);\n"
         );
         {
-            body.append("        ").append(inPckName(clazz)).append(".").append(n).append("(");
+            body.append("        ").append(inPckName(clazz, true)).append(".").append(n).append("(");
             String sep = "";
             for (String arg : args) {
                 body.append(sep);
@@ -1454,7 +1489,7 @@
         );
         if (!onR.onError().isEmpty()) {
             body.append(" else if (type == 3) { /* on close */\n");
-            body.append("        ").append(inPckName(clazz)).append(".").append(onR.onError()).append("(");
+            body.append("        ").append(inPckName(clazz, true)).append(".").append(onR.onError()).append("(");
             body.append("model, null);\n");
             body.append(
                 "        return;" +
@@ -1686,7 +1721,10 @@
         w.write("  }\n");
     }
 
-    private String inPckName(Element e) {
+    private String inPckName(Element e, boolean preferInstance) {
+        if (preferInstance && e.getAnnotation(Model.class).instance()) {
+            return "model.instance";
+        }
         StringBuilder sb = new StringBuilder();
         while (e.getKind() != ElementKind.PACKAGE) {
             if (sb.length() == 0) {
diff -r 2f6f1d20fa7a json/src/test/java/net/java/html/json/MapModelTest.java
--- a/json/src/test/java/net/java/html/json/MapModelTest.java	Wed Dec 02 08:44:31 2015 +0100
+++ b/json/src/test/java/net/java/html/json/MapModelTest.java	Mon Dec 07 23:26:27 2015 +0100
@@ -304,6 +304,38 @@
         assertEquals(p.getAge().get(1).intValue(), 7);
     }
     
+    @Test
+    public void addAge42ThreeTimes() {
+        People p = Models.bind(new People(), c);
+        Map m = (Map)Models.toRaw(p);
+        assertNotNull(m);
+        
+        class Inc implements Runnable {
+            int cnt;
+            
+            @Override
+            public void run() {
+                cnt++;
+            }
+        }
+        Inc incThreeTimes = new Inc();
+        p.onInfoChange(incThreeTimes);
+        
+        p.addAge42();
+        p.addAge42();
+        p.addAge42();
+        final int[] cnt = { 0, 0 };
+        p.readAddAgeCount(cnt, new Runnable() {
+            @Override
+            public void run() {
+                cnt[1] = 1;
+            }
+        });
+        assertEquals(cnt[1], 1, "Callback called");
+        assertEquals(cnt[0], 3, "Internal state kept");
+        assertEquals(incThreeTimes.cnt, 3, "Property change delivered three times");
+    }
+    
     static final class One {
         int changes;
         final PropertyBinding pb;
diff -r 2f6f1d20fa7a json/src/test/java/net/java/html/json/ModelProcessorTest.java
--- a/json/src/test/java/net/java/html/json/ModelProcessorTest.java	Wed Dec 02 08:44:31 2015 +0100
+++ b/json/src/test/java/net/java/html/json/ModelProcessorTest.java	Mon Dec 07 23:26:27 2015 +0100
@@ -386,6 +386,59 @@
         Compile c = Compile.create(html, code, "1.5");
         assertTrue(c.getErrors().isEmpty(), "No errors: " + c.getErrors());
     }
+    
+    @Test public void instanceNeedsDefaultConstructor() throws IOException {
+        String html = "<html><body>"
+            + "</body></html>";
+        String code = "package x.y.z;\n"
+            + "import net.java.html.json.Model;\n"
+            + "import net.java.html.json.Property;\n"
+            + "import net.java.html.json.ComputedProperty;\n"
+            + "@Model(className=\"XModel\", instance=true, properties={\n"
+            + "  @Property(name=\"prop\", type=long.class)\n"
+            + "})\n"
+            + "class X {\n"
+            + "  X(int x) {}\n"
+            + "}\n";
+
+        Compile c = Compile.create(html, code);
+        c.assertError("Needs non-private default constructor when instance=true");
+    }
+    
+    @Test public void instanceNeedsNonPrivateConstructor() throws IOException {
+        String html = "<html><body>"
+            + "</body></html>";
+        String code = "package x.y.z;\n"
+            + "import net.java.html.json.Model;\n"
+            + "import net.java.html.json.Property;\n"
+            + "import net.java.html.json.ComputedProperty;\n"
+            + "@Model(className=\"XModel\", instance=true, properties={\n"
+            + "  @Property(name=\"prop\", type=long.class)\n"
+            + "})\n"
+            + "class X {\n"
+            + "  private X() {}\n"
+            + "}\n";
+
+        Compile c = Compile.create(html, code);
+        c.assertError("Needs non-private default constructor when instance=true");
+    }
+
+    @Test public void instanceNoConstructorIsOK() throws IOException {
+        String html = "<html><body>"
+            + "</body></html>";
+        String code = "package x.y.z;\n"
+            + "import net.java.html.json.Model;\n"
+            + "import net.java.html.json.Property;\n"
+            + "import net.java.html.json.ComputedProperty;\n"
+            + "@Model(className=\"XModel\", instance=true, properties={\n"
+            + "  @Property(name=\"prop\", type=long.class)\n"
+            + "})\n"
+            + "class X {\n"
+            + "}\n";
+
+        Compile c = Compile.create(html, code);
+        c.assertNoErrors();
+    }
 
     @Test public void putNeedsDataArgument() throws Exception {
         needsAnArg("PUT");
diff -r 2f6f1d20fa7a json/src/test/java/net/java/html/json/PersonImpl.java
--- a/json/src/test/java/net/java/html/json/PersonImpl.java	Wed Dec 02 08:44:31 2015 +0100
+++ b/json/src/test/java/net/java/html/json/PersonImpl.java	Mon Dec 07 23:26:27 2015 +0100
@@ -91,26 +91,45 @@
         }
     }
     
-    @Model(className = "People", targetId="myPeople", properties = {
+    @Model(className = "People", instance = true, targetId="myPeople", properties = {
         @Property(array = true, name = "info", type = Person.class),
         @Property(array = true, name = "nicknames", type = String.class),
         @Property(array = true, name = "age", type = int.class),
         @Property(array = true, name = "sex", type = Sex.class)
     })
     public static class PeopleImpl {
-        @ModelOperation static void addAge42(People p) {
+        private int addAgeCount;
+        private Runnable onInfoChange;
+        
+        @ModelOperation void onInfoChange(People self, Runnable r) {
+            onInfoChange = r;
+        }
+        
+        @ModelOperation void addAge42(People p) {
             p.getAge().add(42);
+            addAgeCount++;
         }
 
         @OnReceive(url = "url", method = "WebSocket", data = String.class)
-        static void innerClass(People p, String d) {
+        void innerClass(People p, String d) {
         }
         
-        @Function static void inInnerClass(People p, Person data, int x, double y, String nick) throws IOException {
+        @Function void inInnerClass(People p, Person data, int x, double y, String nick) throws IOException {
             p.getInfo().add(data);
             p.getAge().add(x);
             p.getAge().add((int)y);
             p.getNicknames().add(nick);
         }
+        
+        @ModelOperation void readAddAgeCount(People p, int[] holder, Runnable whenDone) {
+            holder[0] = addAgeCount;
+            whenDone.run();
+        }
+        
+        @OnPropertyChange("age") void infoChange(People p) {
+            if (onInfoChange != null) {
+                onInfoChange.run();
+            }
+        }
     }
 }
diff -r 2f6f1d20fa7a src/main/javadoc/overview.html
--- a/src/main/javadoc/overview.html	Wed Dec 02 08:44:31 2015 +0100
+++ b/src/main/javadoc/overview.html	Mon Dec 07 23:26:27 2015 +0100
@@ -96,6 +96,8 @@
 
         <h3>Improvements in version 1.3</h3>
 
+        {@link net.java.html.json.Model Model classes} can have 
+        {@link net.java.html.json.Model#instance() per-instance private data}.
         {@link net.java.html.json.Model Model classes} can generate
         builder-like construction methods if builder
         {@link net.java.html.json.Model#builder() prefix} is specified.