diff --git a/test/data/html/test-document1.html b/test/data/html/test-document1.html
index 00cc8524..0754a314 100644
--- a/test/data/html/test-document1.html
+++ b/test/data/html/test-document1.html
@@ -13,6 +13,7 @@
 
     <div
         class="test"
+        data-test-type="scan"
         data-element-from-point-selector="span"
         data-caret-range-from-point-selector="span"
         data-start-node-selector="span"
@@ -28,6 +29,7 @@
 
     <div
         class="test"
+        data-test-type="scan"
         data-element-from-point-selector="span"
         data-caret-range-from-point-selector="span"
         data-start-node-selector="span"
@@ -43,6 +45,7 @@
 
     <div
         class="test"
+        data-test-type="scan"
         data-element-from-point-selector="input"
         data-caret-range-from-point-selector="input"
         data-start-node-selector="input"
@@ -59,6 +62,7 @@
 
     <div
         class="test"
+        data-test-type="scan"
         data-element-from-point-selector="textarea"
         data-caret-range-from-point-selector="textarea"
         data-start-node-selector="textarea"
@@ -75,6 +79,7 @@
 
     <div
         class="test"
+        data-test-type="scan"
         data-element-from-point-selector="button"
         data-caret-range-from-point-selector="button"
         data-start-node-selector="button"
@@ -90,6 +95,7 @@
 
     <div
         class="test"
+        data-test-type="scan"
         data-element-from-point-selector="img"
         data-caret-range-from-point-selector="img"
         data-start-node-selector="img"
@@ -102,5 +108,157 @@
         <img src="data:image/gif;base64,R0lGODdhBwAHAIABAAAAAP///ywAAAAABwAHAAACDIRvEaC32FpCbEkKCgA7" alt="よみちゃん" title="よみちゃん" style="width: 70px; height: 70px; image-rendering: crisp-edges; image-rendering: pixelated; display: block;" />
     </div>
 
+    <div
+        class="test"
+        data-test-type="text-source-range-seek"
+        data-seek-node-selector="span:nth-of-type(1)"
+        data-seek-node-is-text="true"
+        data-seek-offset="0"
+        data-seek-length="149"
+        data-seek-direction="forward"
+        data-expected-result-node-selector="span:nth-of-type(1)"
+        data-expected-result-node-is-text="true"
+        data-expected-result-offset="149"
+        data-expected-result-content="
+        あいうえお
+        かきくけこ
+        さしすせそ
+        たちつてと
+        なにぬねの
+        はひふへほ
+        まみむめも
+        や&#x3000;ゆ&#x3000;よ
+        らりるれろ
+        わゐ&#x3000;ゑを
+        "
+    >
+        <span>
+        あいうえお
+        かきくけこ
+        さしすせそ
+        たちつてと
+        なにぬねの
+        はひふへほ
+        まみむめも
+        や&#x3000;ゆ&#x3000;よ
+        らりるれろ
+        わゐ&#x3000;ゑを
+        </span><span>trailing content</span>
+    </div>
+
+    <div
+        class="test"
+        data-test-type="text-source-range-seek"
+        data-seek-node-selector="span:nth-of-type(1)"
+        data-seek-node-is-text="true"
+        data-seek-offset="149"
+        data-seek-length="149"
+        data-seek-direction="backward"
+        data-expected-result-node-selector="span:nth-of-type(1)"
+        data-expected-result-node-is-text="true"
+        data-expected-result-offset="0"
+        data-expected-result-content="
+        あいうえお
+        かきくけこ
+        さしすせそ
+        たちつてと
+        なにぬねの
+        はひふへほ
+        まみむめも
+        や&#x3000;ゆ&#x3000;よ
+        らりるれろ
+        わゐ&#x3000;ゑを
+        "
+    >
+        <span>
+        あいうえお
+        かきくけこ
+        さしすせそ
+        たちつてと
+        なにぬねの
+        はひふへほ
+        まみむめも
+        や&#x3000;ゆ&#x3000;よ
+        らりるれろ
+        わゐ&#x3000;ゑを
+        </span><span>trailing content</span>
+    </div>
+
+    <div
+        class="test"
+        data-test-type="text-source-range-seek"
+        data-seek-node-selector="span:nth-of-type(1)"
+        data-seek-node-is-text="true"
+        data-seek-offset="0"
+        data-seek-length="150"
+        data-seek-direction="forward"
+        data-expected-result-node-selector="span:nth-of-type(2)"
+        data-expected-result-node-is-text="true"
+        data-expected-result-offset="1"
+        data-expected-result-content="
+        あいうえお
+        かきくけこ
+        さしすせそ
+        たちつてと
+        なにぬねの
+        はひふへほ
+        まみむめも
+        や&#x3000;ゆ&#x3000;よ
+        らりるれろ
+        わゐ&#x3000;ゑを
+        t"
+    >
+        <span>
+        あいうえお
+        かきくけこ
+        さしすせそ
+        たちつてと
+        なにぬねの
+        はひふへほ
+        まみむめも
+        や&#x3000;ゆ&#x3000;よ
+        らりるれろ
+        わゐ&#x3000;ゑを
+        </span><span>trailing content</span>
+    </div>
+
+    <div
+        class="test"
+        data-test-type="text-source-range-seek"
+        data-seek-node-selector="span:nth-of-type(2)"
+        data-seek-node-is-text="true"
+        data-seek-offset="1"
+        data-seek-length="150"
+        data-seek-direction="backward"
+        data-expected-result-node-selector="span:nth-of-type(1)"
+        data-expected-result-node-is-text="true"
+        data-expected-result-offset="0"
+        data-expected-result-content="
+        あいうえお
+        かきくけこ
+        さしすせそ
+        たちつてと
+        なにぬねの
+        はひふへほ
+        まみむめも
+        や&#x3000;ゆ&#x3000;よ
+        らりるれろ
+        わゐ&#x3000;ゑを
+        t"
+    >
+        <span>
+        あいうえお
+        かきくけこ
+        さしすせそ
+        たちつてと
+        なにぬねの
+        はひふへほ
+        まみむめも
+        や&#x3000;ゆ&#x3000;よ
+        らりるれろ
+        わゐ&#x3000;ゑを
+        </span><span>trailing content</span>
+    </div>
+
 </body>
 </html>
\ No newline at end of file
diff --git a/test/test-document.js b/test/test-document.js
index 0c3c3d8e..edf6bbea 100644
--- a/test/test-document.js
+++ b/test/test-document.js
@@ -90,16 +90,17 @@ async function testDocument1() {
     );
 
     try {
-        await testDocument1Inner(dom, {docRangeFromPoint, docSentenceExtract, TextSourceRange, TextSourceElement});
+        await testDocumentTextScanningFunctions(dom, {docRangeFromPoint, docSentenceExtract, TextSourceRange, TextSourceElement});
+        await testTextSourceRangeSeekFunctions(dom, {TextSourceRange});
     } finally {
         window.close();
     }
 }
 
-async function testDocument1Inner(dom, {docRangeFromPoint, docSentenceExtract, TextSourceRange, TextSourceElement}) {
+async function testDocumentTextScanningFunctions(dom, {docRangeFromPoint, docSentenceExtract, TextSourceRange, TextSourceElement}) {
     const document = dom.window.document;
 
-    for (const testElement of document.querySelectorAll('.test')) {
+    for (const testElement of document.querySelectorAll('.test[data-test-type=scan]')) {
         // Get test parameters
         let {
             elementFromPointSelector,
@@ -171,6 +172,49 @@ async function testDocument1Inner(dom, {docRangeFromPoint, docSentenceExtract, T
     }
 }
 
+async function testTextSourceRangeSeekFunctions(dom, {TextSourceRange}) {
+    const document = dom.window.document;
+
+    for (const testElement of document.querySelectorAll('.test[data-test-type=text-source-range-seek]')) {
+        // Get test parameters
+        let {
+            seekNodeSelector,
+            seekNodeIsText,
+            seekOffset,
+            seekLength,
+            seekDirection,
+            expectedResultNodeSelector,
+            expectedResultNodeIsText,
+            expectedResultOffset,
+            expectedResultContent
+        } = testElement.dataset;
+
+        seekOffset = parseInt(seekOffset, 10);
+        seekLength = parseInt(seekLength, 10);
+        expectedResultOffset = parseInt(expectedResultOffset, 10);
+
+        let seekNode = testElement.querySelector(seekNodeSelector);
+        if (seekNodeIsText === 'true') {
+            seekNode = seekNode.firstChild;
+        }
+
+        let expectedResultNode = testElement.querySelector(expectedResultNodeSelector);
+        if (expectedResultNodeIsText === 'true') {
+            expectedResultNode = expectedResultNode.firstChild;
+        }
+
+        const {node, offset, content} = (
+            seekDirection === 'forward' ?
+            TextSourceRange.seekForward(seekNode, seekOffset, seekLength) :
+            TextSourceRange.seekBackward(seekNode, seekOffset, seekLength)
+        );
+
+        assert.strictEqual(node, expectedResultNode);
+        assert.strictEqual(offset, expectedResultOffset);
+        assert.strictEqual(content, expectedResultContent);
+    }
+}
+
 
 async function main() {
     await testDocument1();