diff --git a/src/editor/position.js b/src/editor/position.js
index c771482012..5dcb31fe65 100644
--- a/src/editor/position.js
+++ b/src/editor/position.js
@@ -35,4 +35,73 @@ export default class DocumentPosition {
             return this._index - otherPos._index;
         }
     }
+
+    iteratePartsBetween(other, model, callback) {
+        if (this.index === -1 || other.index === -1) {
+            return;
+        }
+        const [startPos, endPos] = this.compare(other) < 0 ? [this, other] : [other, this];
+        if (startPos.index === endPos.index) {
+            callback(model.parts[this.index], startPos.offset, endPos.offset);
+        } else {
+            const firstPart = model.parts[startPos.index];
+            callback(firstPart, startPos.offset, firstPart.text.length);
+            for (let i = startPos.index + 1; i < endPos.index; ++i) {
+                const part = model.parts[i];
+                callback(part, 0, part.text.length);
+            }
+            const lastPart = model.parts[endPos.index];
+            callback(lastPart, 0, endPos.offset);
+        }
+    }
+
+    forwardsWhile(model, predicate) {
+        if (this.index === -1) {
+            return this;
+        }
+
+        let {index, offset} = this;
+        const {parts} = model;
+        while (index < parts.length) {
+            const part = parts[index];
+            while (offset < part.text.length) {
+                if (!predicate(index, offset, part)) {
+                    return new DocumentPosition(index, offset);
+                }
+                offset += 1;
+            }
+            // end reached
+            if (index === (parts.length - 1)) {
+                return new DocumentPosition(index, offset);
+            } else {
+                index += 1;
+                offset = 0;
+            }
+        }
+    }
+
+    backwardsWhile(model, predicate) {
+        if (this.index === -1) {
+            return this;
+        }
+
+        let {index, offset} = this;
+        const parts = model.parts;
+        while (index >= 0) {
+            const part = parts[index];
+            while (offset > 0) {
+                if (!predicate(index, offset - 1, part)) {
+                    return new DocumentPosition(index, offset);
+                }
+                offset -= 1;
+            }
+            // start reached
+            if (index === 0) {
+                return new DocumentPosition(index, offset);
+            } else {
+                index -= 1;
+                offset = parts[index].text.length;
+            }
+        }
+    }
 }
diff --git a/test/editor/position-test.js b/test/editor/position-test.js
new file mode 100644
index 0000000000..7ac4284c60
--- /dev/null
+++ b/test/editor/position-test.js
@@ -0,0 +1,80 @@
+/*
+Copyright 2019 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import expect from 'expect';
+import EditorModel from "../../src/editor/model";
+import {createPartCreator} from "./mock";
+
+function createRenderer() {
+    const render = (c) => {
+        render.caret = c;
+        render.count += 1;
+    };
+    render.count = 0;
+    render.caret = null;
+    return render;
+}
+
+describe('editor/position', function() {
+    it('move first position backward in empty model', function() {
+        const model = new EditorModel([], createPartCreator(), createRenderer());
+        const pos = model.positionForOffset(0, true);
+        const pos2 = pos.backwardsWhile(model, () => true);
+        expect(pos).toBe(pos2);
+    });
+    it('move first position forwards in empty model', function() {
+        const model = new EditorModel([], createPartCreator(), createRenderer());
+        const pos = model.positionForOffset(0, true);
+        const pos2 = pos.forwardsWhile(() => true);
+        expect(pos).toBe(pos2);
+    });
+    it('move forwards within one part', function() {
+        const pc = createPartCreator();
+        const model = new EditorModel([pc.plain("hello")], pc, createRenderer());
+        const pos = model.positionForOffset(1);
+        let n = 3;
+        const pos2 = pos.forwardsWhile(model, () => { n -= 1; return n >= 0; });
+        expect(pos2.index).toBe(0);
+        expect(pos2.offset).toBe(4);
+    });
+    it('move forwards crossing to other part', function() {
+        const pc = createPartCreator();
+        const model = new EditorModel([pc.plain("hello"), pc.plain(" world")], pc, createRenderer());
+        const pos = model.positionForOffset(4);
+        let n = 3;
+        const pos2 = pos.forwardsWhile(model, () => { n -= 1; return n >= 0; });
+        expect(pos2.index).toBe(1);
+        expect(pos2.offset).toBe(2);
+    });
+    it('move backwards within one part', function() {
+        const pc = createPartCreator();
+        const model = new EditorModel([pc.plain("hello")], pc, createRenderer());
+        const pos = model.positionForOffset(4);
+        let n = 3;
+        const pos2 = pos.backwardsWhile(model, () => { n -= 1; return n >= 0; });
+        expect(pos2.index).toBe(0);
+        expect(pos2.offset).toBe(1);
+    });
+    it('move backwards crossing to other part', function() {
+        const pc = createPartCreator();
+        const model = new EditorModel([pc.plain("hello"), pc.plain(" world")], pc, createRenderer());
+        const pos = model.positionForOffset(7);
+        let n = 3;
+        const pos2 = pos.backwardsWhile(model, () => { n -= 1; return n >= 0; });
+        expect(pos2.index).toBe(0);
+        expect(pos2.offset).toBe(4);
+    });
+});