+    normalizeXML: function(nativeNode) {
+        void(nativeNode); // noop
+    },
+
+    toXML: function() {
+        return this.root.toXML();
+    },
+
+    containsNode: function(node) {
+        return this.root && this.root.containsNode(node);
+    },
+
+    getSiblingParents: function(params) {
+        var parents1 = [params.node1].concat(params.node1.parents()).reverse(),
+            parents2 = [params.node2].concat(params.node2.parents()).reverse(),
+            noSiblingParents = null;
+
+        if(parents1.length === 0 || parents2.length === 0 || !(parents1[0].sameNode(parents2[0]))) {
+            return noSiblingParents;
+        }
+
+        var stop = Math.min(parents1.length, parents2.length),
+            i;
+        for(i = 0; i < stop; i++) {
+            if(parents1[i].sameNode(parents2[i])) {
+                continue;
+            }
+            break;
+        }
+        if(i === stop) {
+            i--;
+        }
+        return {node1: parents1[i], node2: parents2[i]};
+    },
+
+    trigger: function() {
+        Backbone.Events.trigger.apply(this, arguments);
+    },
+
+    getNodeInsertion: function(node) {
+        var insertion = {};
+        if(node instanceof DocumentNode) {
+            insertion.ofNode = node;
+            insertion.insertsNew = !this.containsNode(node);
+        } else {
+          insertion.ofNode = this.createDocumentNode(node);
+          insertion.insertsNew = true;
+        }
+        return insertion;
+    },
+
+    registerMethod: function(methodName, method, dstName) {
+        var doc = this;
+        var destination = {
+            document: doc,
+            documentNode: doc._nodeMethods,
+            textNode: doc._textNodeMethods,
+            elementNode: doc._elementNodeMethods
+        }[dstName];
+        registerMethod(methodName, method, destination);
+    },
+
+    registerTransformation: function(desc, name, dstName) {
+        var doc = this;
+        var destination = {
+            document: doc,
+            documentNode: doc._nodeTransformations,
+            textNode: doc._textNodeTransformations,
+            elementNode: doc._elementNodeTransformations
+        }[dstName];
+        registerTransformation(desc, name, destination);
+    },
+
+    registerExtension: function(extension) {
+        var doc = this;
+
+        ['document', 'documentNode', 'elementNode', 'textNode'].forEach(function(dstName) {
+            var dstExtension = extension[dstName];
+            if(dstExtension) {
+                if(dstExtension.methods) {
+                    _.pairs(dstExtension.methods).forEach(function(pair) {
+                        var methodName = pair[0],
+                            method = pair[1];
+
+                        doc.registerMethod(methodName, method, dstName);
+
+                    });
+                }
+
+                if(dstExtension.transformations) {
+                    _.pairs(dstExtension.transformations).forEach(function(pair) {
+                        var name = pair[0],
+                            desc = pair[1];
+                        doc.registerTransformation(desc, name, dstName);
+                    });
+                }
+            }
+        });
+    },
+
+    ifChanged: function(context, action, documentChangedHandler, documentUnchangedHandler) {
+        var hasChanged = false,
+            changeMonitor = function() {
+                hasChanged = true;
+            };
+
+        this.on('change', changeMonitor);
+        action.call(context);
+        this.off('change', changeMonitor);
+        
+        if(hasChanged) {
+            if(documentChangedHandler) {
+                documentChangedHandler.call(context);
+            }
+        } else {
+            if(documentUnchangedHandler) {
+                documentUnchangedHandler.call(context);
+            }
+        }
+    },
+
+    transform: function(Transformation, args) {
+        var toret, transformation;
+
+        if(!this._currentTransaction) {
+            return this.transaction(function() {
+                return this.transform(Transformation, args);
+            }, {context: this});
+        }
+
+        if(typeof Transformation === 'function') {
+            transformation = new Transformation(this, this, args);
+        } else {
+            transformation = Transformation;
+        }
+        if(transformation) {
+            this._transformationLevel++;
+            
+            this.ifChanged(
+                this,
+                function() {
+                    toret = transformation.run({beUndoable:this._transformationLevel === 1});
+                },
+                function() {
+                    if(this._transformationLevel === 1 && !this._undoInProgress) {
+                        this._currentTransaction.pushTransformation(transformation);
+                        this.redoStack = [];
+                    }
+                }
+            );
+
+            this._transformationLevel--;
+            return toret;
+        } else {
+            throw new Error('Transformation ' + transformation + ' doesn\'t exist!');
+        }
+    },
+    undo: function() {
+        var transaction = this.undoStack.pop(),
+            doc = this,
+            transformations, stopAt;
+
+        if(transaction) {
+            this._undoInProgress = true;
+
+            // We will modify this array in a minute so make sure we work on a copy.
+            transformations = transaction.transformations.slice(0);
+
+            if(transformations.length > 1) {
+                // In case of real transactions we don't want to run undo on all of transformations if we don't have to.
+                stopAt = undefined;
+                transformations.some(function(t, idx) {
+                    if(!t.undo && t.getChangeRoot().sameNode(doc.root)) {
+                        stopAt = idx;
+                        return true; //break
+                    }
+                });
+                if(stopAt !== undefined) {
+                    // We will get away with undoing only this transformations as the one at stopAt reverses the whole document.
+                    transformations = transformations.slice(0, stopAt+1);
+                }
+            }
+
+            transformations.reverse();
+            transformations.forEach(function(t) {
+                t.undo();
+            });
+
+            this._undoInProgress = false;
+            this.redoStack.push(transaction);
+        }
+    },
+    redo: function() {
+        var transaction = this.redoStack.pop();
+        if(transaction) {
+            this._transformationLevel++;
+            transaction.transformations.forEach(function(t) {
+                t.run({beUndoable: true});
+            });
+            this._transformationLevel--;
+            this.undoStack.push(transaction);
+        }
+    },
+
+    startTransaction: function(metadata) {
+        if(this._currentTransaction) {
+            throw new Error('Nested transactions not supported!');
+        }
+        this._rollbackBackup = this.root.clone();
+        this._currentTransaction = new Transaction([], metadata);
+    },
+
+    endTransaction: function() {
+        if(!this._currentTransaction) {
+            throw new Error('End of transaction requested, but there is no transaction in progress!');
+        }
+        if(this._currentTransaction.hasTransformations()) {
+            this.undoStack.push(this._currentTransaction);
+        }
+        this._currentTransaction = null;
+    },
+
+    rollbackTransaction: function() {
+        if(!this._currentTransaction) {
+            throw new Error('Transaction rollback requested, but there is no transaction in progress!');
+        }
+        this.replaceRoot(this._rollbackBackup);
+        this._rollbackBackup = null;
+        this._currentTransaction = null;
+        this._transformationLevel = 0;
+    },
+
+    transaction: function(callback, params) {
+        var toret;
+        params = params || {};
+        this.startTransaction(params.metadata);
+        try {
+            toret = callback.call(params.context || this);
+        } catch(e) {
+            if(params.error) {
+                params.error(e);
+            }
+            this.rollbackTransaction();
+            return;
+        }
+        this.endTransaction();
+        if(params.success) {
+            params.success(toret);
+        }
+        return toret;
+    },
+
+    getNodeByPath: function(path) {
+        var toret = this.root;
+        path.forEach(function(idx) {
+            toret = toret.contents()[idx];
+        });
+        return toret;
+    },
+
+    _defineDocumentProperties: function($document) {
+        var doc = this;
+        Object.defineProperty(doc, 'root', {get: function() {
+            if(!$document) {
+                return null;
+            }
+            return doc.createDocumentNode($document[0]);
+        }, configurable: true});
+        Object.defineProperty(doc, 'dom', {get: function() {
+            if(!$document) {
+                return null;
+            }
+            return $document[0];
+        }, configurable: true});