diff -r 6db378e9aa7c json-tck/src/main/java/net/java/html/json/tests/KnockoutTest.java
--- a/json-tck/src/main/java/net/java/html/json/tests/KnockoutTest.java	Thu Jul 02 08:27:47 2015 +0200
+++ b/json-tck/src/main/java/net/java/html/json/tests/KnockoutTest.java	Fri Jul 03 08:34:23 2015 +0200
@@ -136,6 +136,36 @@
             Utils.exposeHTML(KnockoutTest.class, "");
         }
     }
+
+    @KOTest public void modifyComputedProperty() throws Throwable {
+        Object exp = Utils.exposeHTML(KnockoutTest.class,
+            "Full name: <div data-bind='with:firstPerson'>\n"
+                + "<input id='input' data-bind=\"value: fullName\"></input>\n"
+                + "</div>\n"
+        );
+        try {
+            KnockoutModel m = new KnockoutModel();
+            m.getPeople().add(new Person());
+
+            m = Models.bind(m, newContext());
+            m.getFirstPerson().setFirstName("Jarda");
+            m.getFirstPerson().setLastName("Tulach");
+            m.applyBindings();
+
+            String v = getSetInput(null);
+            assertEquals("Jarda Tulach", v, "Value: " + v);
+
+            getSetInput("Mickey Mouse");
+            triggerEvent("input", "change");
+
+            assertEquals("Mickey", m.getFirstPerson().getFirstName(), "First name updated");
+            assertEquals("Mouse", m.getFirstPerson().getLastName(), "Last name updated");
+        } catch (Throwable t) {
+            throw t;
+        } finally {
+            Utils.exposeHTML(KnockoutTest.class, "");
+        }
+    }
     
     @KOTest public void modifyValueAssertChangeInModelOnBoolean() throws Throwable {
         Object exp = Utils.exposeHTML(KnockoutTest.class, 
diff -r 6db378e9aa7c json-tck/src/main/java/net/java/html/json/tests/PersonImpl.java
--- a/json-tck/src/main/java/net/java/html/json/tests/PersonImpl.java	Thu Jul 02 08:27:47 2015 +0200
+++ b/json-tck/src/main/java/net/java/html/json/tests/PersonImpl.java	Fri Jul 03 08:34:23 2015 +0200
@@ -58,10 +58,16 @@
     @Property(name = "address", type = Address.class)
 })
 final class PersonImpl {
-    @ComputedProperty 
+    @ComputedProperty(write = "parseNames")
     public static String fullName(String firstName, String lastName) {
         return firstName + " " + lastName;
     }
+
+    static void parseNames(Person p, String fullName) {
+        String[] arr = fullName.split(" ");
+        p.setFirstName(arr[0]);
+        p.setLastName(arr[1]);
+    }
     
     @ComputedProperty
     public static String sexType(Sex sex) {
diff -r 6db378e9aa7c json/src/main/java/net/java/html/json/ComputedProperty.java
--- a/json/src/main/java/net/java/html/json/ComputedProperty.java	Thu Jul 02 08:27:47 2015 +0200
+++ b/json/src/main/java/net/java/html/json/ComputedProperty.java	Fri Jul 03 08:34:23 2015 +0200
@@ -75,4 +75,31 @@
 @Retention(RetentionPolicy.SOURCE)
 @Target(ElementType.METHOD)
 public @interface ComputedProperty {
+    /** Name of a method to handle changes to the computed property.
+     * By default the computed properties are read-only, however one can
+     * make them mutable by defining a static method that takes
+     * two parameters:
+     * <ol>
+     * <li>the model class</li>
+     * <li>the value - either exactly the return the method annotated
+     *   by this property or a superclass (like {@link Object})</li>
+     * </ol>
+     * Sample code snippet using the <b>write</b> feature of {@link ComputedProperty}
+     * could look like this (assuming the {@link Model model class} named
+     * <em>DataModel</em> has <b>int</b> property <em>value</em>):
+     * <pre>
+     * {@link ComputedProperty @ComputedProperty}(write="setPowerValue")
+     * <b>static int</b> powerValue(<b>int</b> value) {
+     *   <b>return</b> value * value;
+     * }
+     * <b>static void</b> setPowerValue(DataModel m, <b>int</b> value) {
+     *   m.setValue((<b>int</b>){@link Math}.sqrt(value));
+     * }
+     * </pre>
+     * 
+     * @return the name of a method to handle changes to the computed
+     *   property
+     * @since 1.2
+     */
+    public String write() default "";
 }
diff -r 6db378e9aa7c json/src/main/java/org/netbeans/html/json/impl/ModelProcessor.java
--- a/json/src/main/java/org/netbeans/html/json/impl/ModelProcessor.java	Thu Jul 02 08:27:47 2015 +0200
+++ b/json/src/main/java/org/netbeans/html/json/impl/ModelProcessor.java	Fri Jul 03 08:34:23 2015 +0200
@@ -190,7 +190,7 @@
             Map<String, Collection<String>> functionDeps = new HashMap<String, Collection<String>>();
             Prprt[] props = createProps(e, m.properties());
 
-            if (!generateComputedProperties(body, props, e.getEnclosedElements(), propsGetSet, propsDeps)) {
+            if (!generateComputedProperties(className, body, props, e.getEnclosedElements(), propsGetSet, propsDeps)) {
                 ok = false;
             }
             if (!generateOnChange(e, propsDeps, props, className, functionDeps)) {
@@ -626,6 +626,7 @@
     }
 
     private boolean generateComputedProperties(
+        String className,
         Writer w, Prprt[] fixedProps,
         Collection<? extends Element> arr, Collection<GetSet> props,
         Map<String,Collection<String[]>> deps
@@ -646,6 +647,11 @@
                 continue;
             }
             ExecutableElement ee = (ExecutableElement)e;
+            ExecutableElement write = null;
+            if (!cp.write().isEmpty()) {
+                write = findWrite(ee, (TypeElement)e.getEnclosingElement(), cp.write(), className);
+                ok = write != null;
+            }
             final TypeMirror rt = ee.getReturnType();
             final Types tu = processingEnv.getTypeUtils();
             TypeMirror ert = tu.erasure(rt);
@@ -743,13 +749,28 @@
             w.write("    }\n");
             w.write("  }\n");
 
-            props.add(new GetSet(
-                e.getSimpleName().toString(),
-                gs[0],
-                null,
-                tn,
-                true
-            ));
+            if (write == null) {
+                props.add(new GetSet(
+                    e.getSimpleName().toString(),
+                    gs[0],
+                    null,
+                    tn,
+                    true
+                ));
+            } else {
+                w.write("  public void " + gs[4] + "(" + write.getParameters().get(1).asType());
+                w.write(" value) {\n");
+                w.write("    " + fqn(ee.getEnclosingElement().asType(), ee) + '.' + write.getSimpleName() + "(this, value);\n");
+                w.write("  }\n");
+
+                props.add(new GetSet(
+                    e.getSimpleName().toString(),
+                    gs[0],
+                    gs[4],
+                    tn,
+                    false
+                ));
+            }
         }
 
         return ok;
@@ -767,14 +788,16 @@
                 pref + n,
                 null,
                 "a" + n,
-                null
+                null,
+                "set" + n
             };
         }
         return new String[]{
             pref + n,
             "set" + n,
             "a" + n,
-            ""
+            "",
+            "set" + n
         };
     }
 
@@ -2009,4 +2032,55 @@
         return false;
     }
 
+    private ExecutableElement findWrite(ExecutableElement computedPropElem, TypeElement te, String name, String className) {
+        String err = null;
+        METHODS:
+        for (Element e : te.getEnclosedElements()) {
+            if (e.getKind() != ElementKind.METHOD) {
+                continue;
+            }
+            if (!e.getSimpleName().contentEquals(name)) {
+                continue;
+            }
+            if (e.equals(computedPropElem)) {
+                continue;
+            }
+            if (!e.getModifiers().contains(Modifier.STATIC)) {
+                computedPropElem = (ExecutableElement) e;
+                err = "Would have to be static";
+                continue;
+            }
+            ExecutableElement ee = (ExecutableElement) e;
+            TypeMirror retType = computedPropElem.getReturnType();
+            final List<? extends VariableElement> params = ee.getParameters();
+            boolean error = false;
+            if (params.size() != 2) {
+                error = true;
+            } else {
+                String firstType = params.get(0).asType().toString();
+                int lastDot = firstType.lastIndexOf('.');
+                if (lastDot != -1) {
+                    firstType = firstType.substring(lastDot + 1);
+                }
+                if (!firstType.equals(className)) {
+                    error = true;
+                }
+                if (!processingEnv.getTypeUtils().isAssignable(retType, params.get(1).asType())) {
+                    error = true;
+                }
+            }
+            if (error) {
+                computedPropElem = (ExecutableElement) e;
+                err = "Write method first argument needs to be " + className + " and second " + retType + " or Object";
+                continue;
+            }
+            return ee;
+        }
+        if (err == null) {
+            err = "Cannot find " + name + "(" + className + ", value) method in this class";
+        }
+        error(err, computedPropElem);
+        return null;
+    }
+
 }
diff -r 6db378e9aa7c json/src/test/java/net/java/html/json/MapModelTest.java
--- a/json/src/test/java/net/java/html/json/MapModelTest.java	Thu Jul 02 08:27:47 2015 +0200
+++ b/json/src/test/java/net/java/html/json/MapModelTest.java	Fri Jul 03 08:34:23 2015 +0200
@@ -198,6 +198,24 @@
         
         assertEquals(p.getSex(), Sex.FEMALE, "Changed");
     }
+
+    @Test public void changeComputedProperty() {
+        Modelik p = Models.bind(new Modelik(), c);
+        p.setValue(5);
+
+        Map m = (Map)Models.toRaw(p);
+        Object o = m.get("powerValue");
+        assertNotNull(o, "Value is there");
+        assertEquals(o.getClass(), One.class);
+
+        One one = (One)o;
+        assertNotNull(one.pb, "Prop binding specified");
+
+        assertEquals(one.pb.getValue(), 25, "Power of 5");
+
+        one.pb.setValue(16);
+        assertEquals(p.getValue(), 4, "Square root of 16");
+    }
     
     @Test public void removeViaIterator() {
         People p = Models.bind(new People(), c);
diff -r 6db378e9aa7c json/src/test/java/net/java/html/json/ModelProcessorTest.java
--- a/json/src/test/java/net/java/html/json/ModelProcessorTest.java	Thu Jul 02 08:27:47 2015 +0200
+++ b/json/src/test/java/net/java/html/json/ModelProcessorTest.java	Fri Jul 03 08:34:23 2015 +0200
@@ -144,6 +144,72 @@
         }
     }
 
+    @Test public void writeableComputedPropertyMissingWrite() 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\", properties={\n"
+            + "  @Property(name=\"prop\", type=int.class)\n"
+            + "})\n"
+            + "class X {\n"
+            + "    static @ComputedProperty(write=\"setY\") int y(int prop) {\n"
+            + "        return prop;\n"
+            + "    }\n"
+            + "}\n";
+
+        Compile c = Compile.create(html, code);
+        assertFalse(c.getErrors().isEmpty(), "One error: " + c.getErrors());
+        boolean ok = false;
+        StringBuilder msgs = new StringBuilder();
+        for (Diagnostic<? extends JavaFileObject> e : c.getErrors()) {
+            String msg = e.getMessage(Locale.ENGLISH);
+            if (msg.contains("Cannot find setY")) {
+                ok = true;
+            }
+            msgs.append("\n").append(msg);
+        }
+        if (!ok) {
+            fail("Should contain warning about non-static method:" + msgs);
+        }
+    }
+
+    @Test public void writeableComputedPropertyWrongWriteType() 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\", properties={\n"
+            + "  @Property(name=\"prop\", type=int.class)\n"
+            + "})\n"
+            + "class X {\n"
+            + "    static @ComputedProperty(write=\"setY\") int y(int prop) {\n"
+            + "        return prop;\n"
+            + "    }\n"
+            + "    static void setY(String prop) {\n"
+            + "    }\n"
+            + "}\n";
+
+        Compile c = Compile.create(html, code);
+        assertFalse(c.getErrors().isEmpty(), "One error: " + c.getErrors());
+        boolean ok = false;
+        StringBuilder msgs = new StringBuilder();
+        for (Diagnostic<? extends JavaFileObject> e : c.getErrors()) {
+            String msg = e.getMessage(Locale.ENGLISH);
+            if (msg.contains("Write method first argument needs to be XModel and second int or Object")) {
+                ok = true;
+            }
+            msgs.append("\n").append(msg);
+        }
+        if (!ok) {
+            fail("Should contain warning about non-static method:" + msgs);
+        }
+    }
+
     @Test public void computedCantReturnVoid() throws IOException {
         String html = "<html><body>"
             + "</body></html>";
diff -r 6db378e9aa7c json/src/test/java/net/java/html/json/ModelTest.java
--- a/json/src/test/java/net/java/html/json/ModelTest.java	Thu Jul 02 08:27:47 2015 +0200
+++ b/json/src/test/java/net/java/html/json/ModelTest.java	Fri Jul 03 08:34:23 2015 +0200
@@ -173,6 +173,17 @@
         assertTrue(my.mutated.contains("count"), "Count is in there: " + my.mutated);
     }
 
+    @Test public void derivedArrayPropChange() {
+        model.applyBindings();
+        model.setCount(5);
+
+        List<String> arr = model.getRepeat();
+        assertEquals(arr.size(), 5, "Five items: " + arr);
+
+        model.setRepeat(10);
+        assertEquals(model.getCount(), 10, "Changing repeat changes count");
+    }
+
     @Test public void derivedPropertiesAreNotified() {
         model.applyBindings();
 
@@ -255,11 +266,15 @@
     static void doSomething() {
     }
 
-    @ComputedProperty
+    @ComputedProperty(write = "setPowerValue")
     static int powerValue(int value) {
         return value * value;
     }
 
+    static void setPowerValue(Modelik m, int value) {
+        m.setValue((int)Math.sqrt(value));
+    }
+
     @OnPropertyChange({ "powerValue", "unrelated" })
     static void aPropertyChanged(Modelik m, String name) {
         m.setChangedProperty(name);
@@ -278,6 +293,13 @@
         model.setValue(33);
         assertEquals(model.getChangedProperty(), "powerValue", "power property changed");
     }
+    @Test public void changePowerValue() {
+        model.setValue(3);
+        assertEquals(model.getPowerValue(), 9, "Square");
+        model.setPowerValue(16);
+        assertEquals(model.getValue(), 4, "Square root");
+        assertEquals(model.getPowerValue(), 16, "Square changed");
+    }
     @Test public void changeUnrelated() {
         model.setUnrelated(333);
         assertEquals(model.getChangedProperty(), "unrelated", "unrelated changed");
@@ -302,10 +324,13 @@
         return "Not allowed callback!";
     }
 
-    @ComputedProperty
+    @ComputedProperty(write="parseRepeat")
     static List<String> repeat(int count) {
         return Collections.nCopies(count, "Hello");
     }
+    static void parseRepeat(Modelik m, Object v) {
+        m.setCount((Integer)v);
+    }
 
     public @Test void hasPersonPropertyAndComputedFullName() {
         List<Person> arr = model.getPeople();
diff -r 6db378e9aa7c src/main/javadoc/overview.html
--- a/src/main/javadoc/overview.html	Thu Jul 02 08:27:47 2015 +0200
+++ b/src/main/javadoc/overview.html	Fri Jul 03 08:34:23 2015 +0200
@@ -79,7 +79,8 @@
 
         One can control {@link net.java.html.json.OnReceive#headers() HTTP request headers}
         when connecting to server using the {@link net.java.html.json.OnReceive}
-        annotation.
+        annotation. It is possible to have
+        {@link net.java.html.json.ComputedProperty#write() writable computed properties}.
         Bugfix of issues <a target="_blank" href='https://netbeans.org/bugzilla/show_bug.cgi?id=250503'>250503</a>,
         <a target="_blank" href='https://netbeans.org/bugzilla/show_bug.cgi?id=252987'>252987</a>.