diff --git a/src/json-crdt-extensions/cnt/__demos__/docs.ts b/src/json-crdt-extensions/cnt/__demos__/docs.ts
new file mode 100644
index 0000000000..aff2ecb0cd
--- /dev/null
+++ b/src/json-crdt-extensions/cnt/__demos__/docs.ts
@@ -0,0 +1,34 @@
+/* tslint:disable no-console */
+
+/**
+ * Run this demo with:
+ *
+ *     npx nodemon -q -x ts-node src/json-crdt-extensions/cnt/__demos__/docs.ts
+ */
+
+import {Model, s} from '../../../json-crdt';
+import {CntExt} from '..';
+
+console.clear();
+
+const model = Model.withLogicalClock(1234);
+
+model.ext.register(CntExt);
+
+model.api.root({
+  counter: CntExt.new(1),
+});
+console.log(model + '');
+
+// Excess use only ...
+// 2-3 days for finding damages ...
+// ..
+
+const api = model.api.in(['counter']).asExt(CntExt);
+const values = api.view();
+
+console.log(values);
+
+api.inc(10);
+
+console.log(model + '');
diff --git a/src/json-crdt-extensions/index.ts b/src/json-crdt-extensions/index.ts
new file mode 100644
index 0000000000..745c3b1ab5
--- /dev/null
+++ b/src/json-crdt-extensions/index.ts
@@ -0,0 +1,2 @@
+export * from './mval';
+export * from './cnt';
diff --git a/src/json-crdt-extensions/mval/__demos__/docs.ts b/src/json-crdt-extensions/mval/__demos__/docs.ts
new file mode 100644
index 0000000000..95d3d86463
--- /dev/null
+++ b/src/json-crdt-extensions/mval/__demos__/docs.ts
@@ -0,0 +1,30 @@
+/* tslint:disable no-console */
+
+/**
+ * Run this demo with:
+ *
+ *     npx nodemon -q -x ts-node src/json-crdt-extensions/mval/__demos__/docs.ts
+ */
+
+import {Model, s} from '../../../json-crdt';
+import {MvalExt} from '..';
+
+console.clear();
+
+const model = Model.withLogicalClock(1234);
+
+model.ext.register(MvalExt);
+
+model.api.root({
+  score: MvalExt.new(1),
+});
+console.log(model + '');
+
+const api = model.api.in(['score']).asExt(MvalExt);
+const values = api.view();
+
+console.log(values);
+
+api.set(s.con(2));
+
+console.log(model + '');
diff --git a/src/json-crdt-extensions/mval/__demos__/usage.ts b/src/json-crdt-extensions/mval/__demos__/usage.ts
index 638c5814d7..11d6b58cfc 100644
--- a/src/json-crdt-extensions/mval/__demos__/usage.ts
+++ b/src/json-crdt-extensions/mval/__demos__/usage.ts
@@ -7,17 +7,18 @@
  */
 
 import {Model, s} from '../../../json-crdt';
-import {ValueMvExt} from '..';
+import {MvalExt} from '..';
 
 console.clear();
 
 const model = Model.withLogicalClock(1234);
 
-model.ext.register(ValueMvExt);
+model.ext.register(MvalExt);
 
 model.api.root({
   obj: {
-    mv: ValueMvExt.new(s.con(1)),
+    name: s.con('John'),
+    score: MvalExt.new(s.con(1)),
   },
 });
 
@@ -25,7 +26,7 @@ console.log('');
 console.log('Initial value:');
 console.log(model + '');
 
-const api = model.api.in(['obj', 'mv']).asExt(ValueMvExt);
+const api = model.api.in(['obj', 'score']).asExt(MvalExt);
 
 api.set(s.con(5));
 
@@ -35,7 +36,7 @@ console.log(model + '');
 
 const model2 = model.fork();
 
-const api2 = model2.api.in(['obj', 'mv']).asExt(ValueMvExt);
+const api2 = model2.api.in(['obj', 'score']).asExt(MvalExt);
 
 api.set(s.con(10));
 api2.set(s.con(20));
diff --git a/src/json-crdt-extensions/mval/__demos__/view.ts b/src/json-crdt-extensions/mval/__demos__/view.ts
new file mode 100644
index 0000000000..bd2f26f497
--- /dev/null
+++ b/src/json-crdt-extensions/mval/__demos__/view.ts
@@ -0,0 +1,28 @@
+/* tslint:disable no-console */
+
+/**
+ * Run this demo with:
+ *
+ *     npx nodemon -q -x ts-node src/json-crdt-extensions/mval/__demos__/view.ts
+ */
+
+import {Model, s} from '../../../json-crdt';
+import {MvalExt} from '..';
+
+console.clear();
+
+const model = Model.withLogicalClock(1234);
+
+model.ext.register(MvalExt);
+
+model.api.root(MvalExt.new(s.con(1)));
+
+console.log('');
+console.log('Model with extension:');
+console.log(model + '');
+
+const model2 = Model.fromBinary(model.toBinary());
+
+console.log('');
+console.log('Model not aware of extension:');
+console.log(model2 + '');
diff --git a/src/json-crdt-extensions/mval/__tests__/ValueMv.spec.ts b/src/json-crdt-extensions/mval/__tests__/MvalExt.spec.ts
similarity index 74%
rename from src/json-crdt-extensions/mval/__tests__/ValueMv.spec.ts
rename to src/json-crdt-extensions/mval/__tests__/MvalExt.spec.ts
index 97cffa0eb9..d94e8bc45e 100644
--- a/src/json-crdt-extensions/mval/__tests__/ValueMv.spec.ts
+++ b/src/json-crdt-extensions/mval/__tests__/MvalExt.spec.ts
@@ -1,14 +1,14 @@
-import {ValueMvExt} from '..';
+import {MvalExt} from '..';
 import {Model} from '../../../json-crdt/model';
 
 test('can set new values in single fork', () => {
   const model = Model.withLogicalClock();
-  model.ext.register(ValueMvExt);
+  model.ext.register(MvalExt);
   model.api.root({
-    mv: ValueMvExt.new(1),
+    mv: MvalExt.new(1),
   });
   expect(model.view()).toEqual({mv: [1]});
-  const register = model.api.in(['mv']).asExt(ValueMvExt);
+  const register = model.api.in(['mv']).asExt(MvalExt);
   register.set(2);
   expect(model.view()).toEqual({mv: [2]});
   register.set(3);
@@ -17,11 +17,11 @@ test('can set new values in single fork', () => {
 
 test('removes tombstones on insert', () => {
   const model = Model.withLogicalClock();
-  model.ext.register(ValueMvExt);
+  model.ext.register(MvalExt);
   model.api.root({
-    mv: ValueMvExt.new(1),
+    mv: MvalExt.new(1),
   });
-  const register = model.api.in(['mv']).asExt(ValueMvExt);
+  const register = model.api.in(['mv']).asExt(MvalExt);
   expect(register.node.data.size()).toBe(1);
   register.set(2);
   expect(register.node.data.size()).toBe(1);
@@ -33,13 +33,13 @@ test('removes tombstones on insert', () => {
 
 test('contains two values when two forks set value concurrently', () => {
   const model1 = Model.withLogicalClock();
-  model1.ext.register(ValueMvExt);
+  model1.ext.register(MvalExt);
   model1.api.root({
-    mv: ValueMvExt.new(1),
+    mv: MvalExt.new(1),
   });
   const model2 = model1.fork();
-  const register1 = model1.api.in(['mv']).asExt(ValueMvExt);
-  const register2 = model2.api.in(['mv']).asExt(ValueMvExt);
+  const register1 = model1.api.in(['mv']).asExt(MvalExt);
+  const register2 = model2.api.in(['mv']).asExt(MvalExt);
   register1.set(2);
   register2.set(3);
   expect(model1.view()).toEqual({mv: [2]});
@@ -56,13 +56,13 @@ test('contains two values when two forks set value concurrently', () => {
 
 test('contains one value when a fork overwrites a register', () => {
   const model1 = Model.withLogicalClock();
-  model1.ext.register(ValueMvExt);
+  model1.ext.register(MvalExt);
   model1.api.root({
-    mv: ValueMvExt.new(1),
+    mv: MvalExt.new(1),
   });
   const model2 = model1.fork();
-  const register1 = model1.api.in(['mv']).asExt(ValueMvExt);
-  const register2 = model2.api.in(['mv']).asExt(ValueMvExt);
+  const register1 = model1.api.in(['mv']).asExt(MvalExt);
+  const register2 = model2.api.in(['mv']).asExt(MvalExt);
   register1.set(2);
   register2.set(3);
   model1.applyPatch(model2.api.flush());
diff --git a/src/json-crdt-extensions/mval/index.ts b/src/json-crdt-extensions/mval/index.ts
index 5e1c7a074e..b1e64acc9f 100644
--- a/src/json-crdt-extensions/mval/index.ts
+++ b/src/json-crdt-extensions/mval/index.ts
@@ -7,7 +7,7 @@ import type {ITimestampStruct} from '../../json-crdt-patch/clock';
 import type {ArrNode} from '../../json-crdt/nodes/arr/ArrNode';
 import type {ExtensionDefinition} from '../../json-crdt';
 
-export const ValueMvExt: ExtensionDefinition<ArrNode, ValueMv, ValueMvApi> = {
+export const MvalExt: ExtensionDefinition<ArrNode, ValueMv, ValueMvApi> = {
   id: ExtensionId.mval,
   name: 'mval',
   new: (value: unknown | ITimestampStruct) =>
diff --git a/src/json-crdt/extensions/Extensions.ts b/src/json-crdt/extensions/Extensions.ts
index e3fd7e4ebb..65143f027b 100644
--- a/src/json-crdt/extensions/Extensions.ts
+++ b/src/json-crdt/extensions/Extensions.ts
@@ -28,7 +28,7 @@ export class Extensions implements Printable {
       .map((k) => +k)
       .sort();
     return (
-      this.constructor.name +
+      'extensions' +
       printTree(
         tab,
         keys.map((k) => (tab) => `${k}: ${this.ext[k].name}`),
diff --git a/src/json-crdt/extensions/README.md b/src/json-crdt/extensions/README.md
new file mode 100644
index 0000000000..eee667078c
--- /dev/null
+++ b/src/json-crdt/extensions/README.md
@@ -0,0 +1,29 @@
+# Extensions
+
+Extensions allow to create new node types out of the existing built-in types:
+`con`, `val`, `obj`, `vec`, `str`, `bin`, `arr`.
+
+Each extension has a globally unique ID, which is an 8-bit unsigned integer.
+Thus, only 256 extensions can be defined at the same time.
+
+Extensions do not modify in any shape the JSON CRDT, nor JSON CRDT Patch
+protocols, instead they build on top of the `vec` node type. An extension node
+is a `vec` node with a specific structure, and a specific interpretation of the
+elements of the `vec` node.
+
+An extension `vec` node follows the following structure: it is a 2-tuple, where
+the first element in the extension *header* and the second element is the
+extension *payload*.
+
+The extension *header* is a `con` node, which holds a 3 byte `Uint8Array` with
+the following octets: (1) the extension ID, (2) the session ID modulo 256, and
+(3) the time sequence modulo 256.
+
+The extension *payload* is any JSON CRDT node with any value, which is specific
+to the extension.
+
+```
+vec
+├─ 0: con Uin8Array { <ext_id>, <sid_mod_256>, <time_mod_256> }
+└─ 1: any
+```
diff --git a/src/json-crdt/nodes/vec/__tests__/extension.spec.ts b/src/json-crdt/nodes/vec/__tests__/extension.spec.ts
index 8e6ae482cc..d5f4a78ac7 100644
--- a/src/json-crdt/nodes/vec/__tests__/extension.spec.ts
+++ b/src/json-crdt/nodes/vec/__tests__/extension.spec.ts
@@ -1,16 +1,16 @@
-import {ValueMvExt} from '../../../../json-crdt-extensions/mval';
+import {MvalExt} from '../../../../json-crdt-extensions/mval';
 import {konst} from '../../../../json-crdt-patch/builder/Konst';
 import {Model} from '../../../../json-crdt/model';
 
 test('can specify extension name', () => {
-  expect(ValueMvExt.name).toBe('mval');
+  expect(MvalExt.name).toBe('mval');
 });
 
 test('can create a new multi-value register', () => {
   const model = Model.withLogicalClock();
-  model.ext.register(ValueMvExt);
+  model.ext.register(MvalExt);
   model.api.root({
-    mv: ValueMvExt.new(),
+    mv: MvalExt.new(),
   });
   expect(model.view()).toEqual({
     mv: [],
@@ -19,9 +19,9 @@ test('can create a new multi-value register', () => {
 
 test('can provide initial value', () => {
   const model = Model.withLogicalClock();
-  model.ext.register(ValueMvExt);
+  model.ext.register(MvalExt);
   model.api.root({
-    mv: ValueMvExt.new({foo: 'bar'}),
+    mv: MvalExt.new({foo: 'bar'}),
   });
   expect(model.view()).toEqual({
     mv: [{foo: 'bar'}],
@@ -30,22 +30,22 @@ test('can provide initial value', () => {
 
 test('can read view from node or API node', () => {
   const model = Model.withLogicalClock();
-  model.ext.register(ValueMvExt);
+  model.ext.register(MvalExt);
   model.api.root({
-    mv: ValueMvExt.new('foo'),
+    mv: MvalExt.new('foo'),
   });
-  const api = model.api.in('mv').asExt(ValueMvExt);
+  const api = model.api.in('mv').asExt(MvalExt);
   expect(api.view()).toEqual(['foo']);
   expect(api.node.view()).toEqual(['foo']);
 });
 
 test('exposes API to edit extension data', () => {
   const model = Model.withLogicalClock();
-  model.ext.register(ValueMvExt);
+  model.ext.register(MvalExt);
   model.api.root({
-    mv: ValueMvExt.new(),
+    mv: MvalExt.new(),
   });
-  const nodeApi = model.api.in('mv').asExt(ValueMvExt);
+  const nodeApi = model.api.in('mv').asExt(MvalExt);
   nodeApi.set(konst('lol'));
   expect(model.view()).toEqual({
     mv: ['lol'],
@@ -55,9 +55,9 @@ test('exposes API to edit extension data', () => {
 describe('extension validity checks', () => {
   test('does not treat ArrNode as extension if header is too long', () => {
     const model = Model.withLogicalClock();
-    model.ext.register(ValueMvExt);
+    model.ext.register(MvalExt);
     model.api.root({
-      mv: ValueMvExt.new(),
+      mv: MvalExt.new(),
     });
     const buf = new Uint8Array(4);
     buf.set(model.api.const(['mv', 0]).node.view() as Uint8Array, 0);
@@ -70,9 +70,9 @@ describe('extension validity checks', () => {
 
   test('does not treat ArrNode as extension if header sid is wrong', () => {
     const model = Model.withLogicalClock();
-    model.ext.register(ValueMvExt);
+    model.ext.register(MvalExt);
     model.api.root({
-      mv: ValueMvExt.new(),
+      mv: MvalExt.new(),
     });
     const buf = model.api.const(['mv', 0]).node.view() as Uint8Array;
     buf[1] += 1;
@@ -84,9 +84,9 @@ describe('extension validity checks', () => {
 
   test('does not treat ArrNode as extension if header time is wrong', () => {
     const model = Model.withLogicalClock();
-    model.ext.register(ValueMvExt);
+    model.ext.register(MvalExt);
     model.api.root({
-      mv: ValueMvExt.new(),
+      mv: MvalExt.new(),
     });
     const buf = model.api.const(['mv', 0]).node.view() as Uint8Array;
     buf[2] += 1;