Use DOMTextScanner (#536)

* Use DOMTextScanner instead of TextSourceRange.seek*

* Move getNodesInRange to dom.js

* Move anyNodeMatchesSelector to dom.js

* Remove unused functions

* Update tests

* Add layoutAwareScan option

* Use layoutAwareScan for source and sentence scanning

* Remove unused IGNORE_TEXT_PATTERN

15 files changed, 102 insertions, 247 deletions

diff --git a/ext/bg/data/options-schema.json b/ext/bg/data/options-schema.json
index 0379fa75..5885e036 100644
--- a/ext/bg/data/options-schema.json
+++ b/ext/bg/data/options-schema.json
@@ -321,7 +321,8 @@
                                     "enablePopupSearch",
                                     "enableOnPopupExpressions",
                                     "enableOnSearchPage",
-                                    "enableSearchTags"
+                                    "enableSearchTags",
+                                    "layoutAwareScan"
                                 ],
                                 "properties": {
                                     "middleMouse": {
@@ -383,6 +384,10 @@
                                     "enableSearchTags": {
                                         "type": "boolean",
                                         "default": false
+                                    },
+                                    "layoutAwareScan": {
+                                        "type": "boolean",
+                                        "default": false
                                     }
                                 }
                             },
diff --git a/ext/bg/js/options.js b/ext/bg/js/options.js
index 97368a0b..170e4799 100644
--- a/ext/bg/js/options.js
+++ b/ext/bg/js/options.js
@@ -203,7 +203,8 @@ function profileOptionsCreateDefaults() {
             enablePopupSearch: false,
             enableOnPopupExpressions: false,
             enableOnSearchPage: true,
-            enableSearchTags: false
+            enableSearchTags: false,
+            layoutAwareScan: false
         },
 
         translation: {
diff --git a/ext/bg/js/search-query-parser.js b/ext/bg/js/search-query-parser.js
index addfc686..97e98b40 100644
--- a/ext/bg/js/search-query-parser.js
+++ b/ext/bg/js/search-query-parser.js
@@ -75,15 +75,17 @@ class QueryParser {
     async _search(textSource, cause) {
         if (textSource === null) { return null; }
 
-        const searchText = this._textScanner.getTextSourceContent(textSource, this._options.scanning.length);
+        const {length: scanLength, layoutAwareScan} = this._options.scanning;
+        const searchText = this._textScanner.getTextSourceContent(textSource, scanLength, layoutAwareScan);
         if (searchText.length === 0) { return null; }
 
         const {definitions, length} = await api.termsFind(searchText, {}, this._getOptionsContext());
         if (definitions.length === 0) { return null; }
 
-        const sentence = docSentenceExtract(textSource, this._options.anki.sentenceExt);
+        const sentenceExtent = this._options.anki.sentenceExt;
+        const sentence = docSentenceExtract(textSource, sentenceExtent, layoutAwareScan);
 
-        textSource.setEndOffset(length);
+        textSource.setEndOffset(length, layoutAwareScan);
 
         this._setContent('terms', {definitions, context: {
             focus: false,
diff --git a/ext/bg/search.html b/ext/bg/search.html
index de08cdae..4a28dd88 100644
--- a/ext/bg/search.html
+++ b/ext/bg/search.html
@@ -79,6 +79,7 @@
         <script src="/bg/js/dictionary.js"></script>
         <script src="/bg/js/handlebars.js"></script>
         <script src="/fg/js/document.js"></script>
+        <script src="/fg/js/dom-text-scanner.js"></script>
         <script src="/fg/js/source.js"></script>
         <script src="/mixed/js/audio-system.js"></script>
         <script src="/mixed/js/display-context.js"></script>
diff --git a/ext/bg/settings-popup-preview.html b/ext/bg/settings-popup-preview.html
index fe92f24f..5eecd005 100644
--- a/ext/bg/settings-popup-preview.html
+++ b/ext/bg/settings-popup-preview.html
@@ -126,6 +126,7 @@
         <script src="/mixed/js/text-scanner.js"></script>
 
         <script src="/fg/js/document.js"></script>
+        <script src="/fg/js/dom-text-scanner.js"></script>
         <script src="/fg/js/popup.js"></script>
         <script src="/fg/js/source.js"></script>
         <script src="/fg/js/popup-factory.js"></script>
diff --git a/ext/bg/settings.html b/ext/bg/settings.html
index 118a13b9..77b61aef 100644
--- a/ext/bg/settings.html
+++ b/ext/bg/settings.html
@@ -400,6 +400,10 @@
                     <label><input type="checkbox" id="auto-hide-results" data-setting="scanning.autoHideResults"> Automatically hide results</label>
                 </div>
 
+                <div class="checkbox">
+                    <label><input type="checkbox" id="layout-aware-scan" data-setting="scanning.layoutAwareScan"> Layout-aware scan</label>
+                </div>
+
                 <div class="checkbox options-advanced">
                     <label><input type="checkbox" id="deep-dom-scan" data-setting="scanning.deepDomScan"> Deep DOM scan</label>
                 </div>
diff --git a/ext/fg/float.html b/ext/fg/float.html
index 17dbcc6d..3e41cde5 100644
--- a/ext/fg/float.html
+++ b/ext/fg/float.html
@@ -46,6 +46,7 @@
         <script src="/mixed/js/japanese.js"></script>
 
         <script src="/fg/js/document.js"></script>
+        <script src="/fg/js/dom-text-scanner.js"></script>
         <script src="/fg/js/source.js"></script>
         <script src="/mixed/js/audio-system.js"></script>
         <script src="/mixed/js/display-context.js"></script>
diff --git a/ext/fg/js/document.js b/ext/fg/js/document.js
index d639bc86..c288502c 100644
--- a/ext/fg/js/document.js
+++ b/ext/fg/js/document.js
@@ -17,6 +17,7 @@
 
 /* global
  * DOM
+ * DOMTextScanner
  * TextSourceElement
  * TextSourceRange
  */
@@ -152,14 +153,14 @@ function docRangeFromPoint(x, y, deepDomScan) {
     }
 }
 
-function docSentenceExtract(source, extent) {
+function docSentenceExtract(source, extent, layoutAwareScan) {
     const quotesFwd = {'「': '」', '『': '』', "'": "'", '"': '"'};
     const quotesBwd = {'」': '「', '』': '『', "'": "'", '"': '"'};
     const terminators = '…。．.？?！!';
 
     const sourceLocal = source.clone();
-    const position = sourceLocal.setStartOffset(extent);
-    sourceLocal.setEndOffset(extent * 2 - position, true);
+    const position = sourceLocal.setStartOffset(extent, layoutAwareScan);
+    sourceLocal.setEndOffset(extent * 2 - position, layoutAwareScan, true);
     const content = sourceLocal.text();
 
     let quoteStack = [];
@@ -232,7 +233,7 @@ function isPointInRange(x, y, range) {
     const nodePre = range.endContainer;
     const offsetPre = range.endOffset;
     try {
-        const {node, offset, content} = TextSourceRange.seekForward(range.endContainer, range.endOffset, 1);
+        const {node, offset, content} = new DOMTextScanner(range.endContainer, range.endOffset, true, false).seek(1);
         range.setEnd(node, offset);
 
         if (!isWhitespace(content) && DOM.isPointInAnyRect(x, y, range.getClientRects())) {
@@ -243,7 +244,7 @@ function isPointInRange(x, y, range) {
     }
 
     // Scan backward
-    const {node, offset, content} = TextSourceRange.seekBackward(range.startContainer, range.startOffset, 1);
+    const {node, offset, content} = new DOMTextScanner(range.startContainer, range.startOffset, true, false).seek(-1);
     range.setStart(node, offset);
 
     if (!isWhitespace(content) && DOM.isPointInAnyRect(x, y, range.getClientRects())) {
diff --git a/ext/fg/js/frontend.js b/ext/fg/js/frontend.js
index 70bd8a48..ab455c09 100644
--- a/ext/fg/js/frontend.js
+++ b/ext/fg/js/frontend.js
@@ -258,32 +258,36 @@ class Frontend {
     }
 
     async _findTerms(textSource, optionsContext) {
-        const searchText = this._textScanner.getTextSourceContent(textSource, this._options.scanning.length);
+        const {length: scanLength, layoutAwareScan} = this._options.scanning;
+        const searchText = this._textScanner.getTextSourceContent(textSource, scanLength, layoutAwareScan);
         if (searchText.length === 0) { return null; }
 
         const {definitions, length} = await api.termsFind(searchText, {}, optionsContext);
         if (definitions.length === 0) { return null; }
 
-        textSource.setEndOffset(length);
+        textSource.setEndOffset(length, layoutAwareScan);
 
         return {definitions, type: 'terms'};
     }
 
     async _findKanji(textSource, optionsContext) {
-        const searchText = this._textScanner.getTextSourceContent(textSource, 1);
+        const layoutAwareScan = this._options.scanning.layoutAwareScan;
+        const searchText = this._textScanner.getTextSourceContent(textSource, 1, layoutAwareScan);
         if (searchText.length === 0) { return null; }
 
         const definitions = await api.kanjiFind(searchText, optionsContext);
         if (definitions.length === 0) { return null; }
 
-        textSource.setEndOffset(1);
+        textSource.setEndOffset(1, layoutAwareScan);
 
         return {definitions, type: 'kanji'};
     }
 
     _showContent(textSource, focus, definitions, type, optionsContext) {
         const {url} = optionsContext;
-        const sentence = docSentenceExtract(textSource, this._options.anki.sentenceExt);
+        const sentenceExtent = this._options.anki.sentenceExt;
+        const layoutAwareScan = this._options.scanning.layoutAwareScan;
+        const sentence = docSentenceExtract(textSource, sentenceExtent, layoutAwareScan);
         this._showPopupContent(
             textSource,
             optionsContext,
diff --git a/ext/fg/js/source.js b/ext/fg/js/source.js
index fa4706f2..38810f07 100644
--- a/ext/fg/js/source.js
+++ b/ext/fg/js/source.js
@@ -15,9 +15,9 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
-// \u200c (Zero-width non-joiner) appears on Google Docs from Chrome 76 onwards
-const IGNORE_TEXT_PATTERN = /\u200c/;
-
+/* global
+ * DOMTextScanner
+ */
 
 /*
  * TextSourceRange
@@ -46,19 +46,19 @@ class TextSourceRange {
         return this.content;
     }
 
-    setEndOffset(length, fromEnd=false) {
+    setEndOffset(length, layoutAwareScan, fromEnd=false) {
         const state = (
             fromEnd ?
-            TextSourceRange.seekForward(this.range.endContainer, this.range.endOffset, length) :
-            TextSourceRange.seekForward(this.range.startContainer, this.range.startOffset, length)
+            new DOMTextScanner(this.range.endContainer, this.range.endOffset, !layoutAwareScan, layoutAwareScan).seek(length) :
+            new DOMTextScanner(this.range.startContainer, this.range.startOffset, !layoutAwareScan, layoutAwareScan).seek(length)
         );
         this.range.setEnd(state.node, state.offset);
         this.content = (fromEnd ? this.content + state.content : state.content);
         return length - state.remainder;
     }
 
-    setStartOffset(length) {
-        const state = TextSourceRange.seekBackward(this.range.startContainer, this.range.startOffset, length);
+    setStartOffset(length, layoutAwareScan) {
+        const state = new DOMTextScanner(this.range.startContainer, this.range.startOffset, !layoutAwareScan, layoutAwareScan).seek(-length);
         this.range.setStart(state.node, state.offset);
         this.rangeStartOffset = this.range.startOffset;
         this.content = state.content + this.content;
@@ -110,154 +110,6 @@ class TextSourceRange {
         }
     }
 
-    static shouldEnter(node) {
-        switch (node.nodeName.toUpperCase()) {
-            case 'RT':
-            case 'SCRIPT':
-            case 'STYLE':
-                return false;
-        }
-
-        const style = window.getComputedStyle(node);
-        return !(
-            style.visibility === 'hidden' ||
-            style.display === 'none' ||
-            parseFloat(style.fontSize) === 0
-        );
-    }
-
-    static getRubyElement(node) {
-        node = TextSourceRange.getParentElement(node);
-        if (node !== null && node.nodeName.toUpperCase() === 'RT') {
-            node = node.parentNode;
-            return (node !== null && node.nodeName.toUpperCase() === 'RUBY') ? node : null;
-        }
-        return null;
-    }
-
-    static seekForward(node, offset, length) {
-        const state = {node, offset, remainder: length, content: ''};
-        if (length <= 0) {
-            return state;
-        }
-
-        const TEXT_NODE = Node.TEXT_NODE;
-        const ELEMENT_NODE = Node.ELEMENT_NODE;
-        let resetOffset = false;
-
-        const ruby = TextSourceRange.getRubyElement(node);
-        if (ruby !== null) {
-            node = ruby;
-            resetOffset = true;
-        }
-
-        while (node !== null) {
-            let visitChildren = true;
-            const nodeType = node.nodeType;
-
-            if (nodeType === TEXT_NODE) {
-                state.node = node;
-                if (TextSourceRange.seekForwardTextNode(state, resetOffset)) {
-                    break;
-                }
-                resetOffset = true;
-            } else if (nodeType === ELEMENT_NODE) {
-                visitChildren = TextSourceRange.shouldEnter(node);
-            }
-
-            node = TextSourceRange.getNextNode(node, visitChildren);
-        }
-
-        return state;
-    }
-
-    static seekForwardTextNode(state, resetOffset) {
-        const nodeValue = state.node.nodeValue;
-        const nodeValueLength = nodeValue.length;
-        let content = state.content;
-        let offset = resetOffset ? 0 : state.offset;
-        let remainder = state.remainder;
-        let result = false;
-
-        for (; offset < nodeValueLength; ++offset) {
-            const c = nodeValue[offset];
-            if (!IGNORE_TEXT_PATTERN.test(c)) {
-                content += c;
-                if (--remainder <= 0) {
-                    result = true;
-                    ++offset;
-                    break;
-                }
-            }
-        }
-
-        state.offset = offset;
-        state.content = content;
-        state.remainder = remainder;
-        return result;
-    }
-
-    static seekBackward(node, offset, length) {
-        const state = {node, offset, remainder: length, content: ''};
-        if (length <= 0) {
-            return state;
-        }
-
-        const TEXT_NODE = Node.TEXT_NODE;
-        const ELEMENT_NODE = Node.ELEMENT_NODE;
-        let resetOffset = false;
-
-        const ruby = TextSourceRange.getRubyElement(node);
-        if (ruby !== null) {
-            node = ruby;
-            resetOffset = true;
-        }
-
-        while (node !== null) {
-            let visitChildren = true;
-            const nodeType = node.nodeType;
-
-            if (nodeType === TEXT_NODE) {
-                state.node = node;
-                if (TextSourceRange.seekBackwardTextNode(state, resetOffset)) {
-                    break;
-                }
-                resetOffset = true;
-            } else if (nodeType === ELEMENT_NODE) {
-                visitChildren = TextSourceRange.shouldEnter(node);
-            }
-
-            node = TextSourceRange.getPreviousNode(node, visitChildren);
-        }
-
-        return state;
-    }
-
-    static seekBackwardTextNode(state, resetOffset) {
-        const nodeValue = state.node.nodeValue;
-        let content = state.content;
-        let offset = resetOffset ? nodeValue.length : state.offset;
-        let remainder = state.remainder;
-        let result = false;
-
-        for (; offset > 0; --offset) {
-            const c = nodeValue[offset - 1];
-            if (!IGNORE_TEXT_PATTERN.test(c)) {
-                content = c + content;
-                if (--remainder <= 0) {
-                    result = true;
-                    --offset;
-                    break;
-                }
-            }
-        }
-
-        state.offset = offset;
-        state.content = content;
-        state.remainder = remainder;
-        return result;
-    }
-
     static getParentElement(node) {
         while (node !== null && node.nodeType !== Node.ELEMENT_NODE) {
             node = node.parentNode;
@@ -290,66 +142,6 @@ class TextSourceRange {
                 return writingMode;
         }
     }
-
-    static getNodesInRange(range) {
-        const end = range.endContainer;
-        const nodes = [];
-        for (let node = range.startContainer; node !== null; node = TextSourceRange.getNextNode(node, true)) {
-            nodes.push(node);
-            if (node === end) { break; }
-        }
-        return nodes;
-    }
-
-    static getNextNode(node, visitChildren) {
-        let next = visitChildren ? node.firstChild : null;
-        if (next === null) {
-            while (true) {
-                next = node.nextSibling;
-                if (next !== null) { break; }
-
-                next = node.parentNode;
-                if (next === null) { break; }
-
-                node = next;
-            }
-        }
-        return next;
-    }
-
-    static getPreviousNode(node, visitChildren) {
-        let next = visitChildren ? node.lastChild : null;
-        if (next === null) {
-            while (true) {
-                next = node.previousSibling;
-                if (next !== null) { break; }
-
-                next = node.parentNode;
-                if (next === null) { break; }
-
-                node = next;
-            }
-        }
-        return next;
-    }
-
-    static anyNodeMatchesSelector(nodeList, selector) {
-        for (const node of nodeList) {
-            if (TextSourceRange.nodeMatchesSelector(node, selector)) {
-                return true;
-            }
-        }
-        return false;
-    }
-
-    static nodeMatchesSelector(node, selector) {
-        for (; node !== null; node = node.parentNode) {
-            if (node.nodeType === Node.ELEMENT_NODE) {
-                return node.matches(selector);
-            }
-        }
-        return false;
-    }
 }
 
 
diff --git a/ext/manifest.json b/ext/manifest.json
index 75334675..4d4f0c06 100644
--- a/ext/manifest.json
+++ b/ext/manifest.json
@@ -42,6 +42,7 @@
             "mixed/js/dynamic-loader.js",
             "mixed/js/text-scanner.js",
             "fg/js/document.js",
+            "fg/js/dom-text-scanner.js",
             "fg/js/popup.js",
             "fg/js/source.js",
             "fg/js/popup-factory.js",
diff --git a/ext/mixed/js/display.js b/ext/mixed/js/display.js
index 90fd1037..1d699706 100644
--- a/ext/mixed/js/display.js
+++ b/ext/mixed/js/display.js
@@ -236,7 +236,9 @@ class Display {
             const {textSource, definitions} = termLookupResults;
 
             const scannedElement = e.target;
-            const sentence = docSentenceExtract(textSource, this.options.anki.sentenceExt);
+            const sentenceExtent = this.options.anki.sentenceExt;
+            const layoutAwareScan = this.options.scanning.layoutAwareScan;
+            const sentence = docSentenceExtract(textSource, sentenceExtent, layoutAwareScan);
 
             this.context.update({
                 index: this.entryIndexFind(scannedElement),
@@ -273,21 +275,22 @@ class Display {
         try {
             e.preventDefault();
 
-            const textSource = docRangeFromPoint(e.clientX, e.clientY, this.options.scanning.deepDomScan);
+            const {length: scanLength, deepDomScan: deepScan, layoutAwareScan} = this.options.scanning;
+            const textSource = docRangeFromPoint(e.clientX, e.clientY, deepScan);
             if (textSource === null) {
                 return false;
             }
 
             let definitions, length;
             try {
-                textSource.setEndOffset(this.options.scanning.length);
+                textSource.setEndOffset(scanLength, layoutAwareScan);
 
                 ({definitions, length} = await api.termsFind(textSource.text(), {}, this.getOptionsContext()));
                 if (definitions.length === 0) {
                     return false;
                 }
 
-                textSource.setEndOffset(length);
+                textSource.setEndOffset(length, layoutAwareScan);
             } finally {
                 textSource.cleanup();
             }
diff --git a/ext/mixed/js/dom.js b/ext/mixed/js/dom.js
index 0e8f4462..05764443 100644
--- a/ext/mixed/js/dom.js
+++ b/ext/mixed/js/dom.js
@@ -86,4 +86,42 @@ class DOM {
             null
         );
     }
+
+    static getNodesInRange(range) {
+        const end = range.endContainer;
+        const nodes = [];
+        for (let node = range.startContainer; node !== null; node = DOM.getNextNode(node)) {
+            nodes.push(node);
+            if (node === end) { break; }
+        }
+        return nodes;
+    }
+
+    static getNextNode(node) {
+        let next = node.firstChild;
+        if (next === null) {
+            while (true) {
+                next = node.nextSibling;
+                if (next !== null) { break; }
+
+                next = node.parentNode;
+                if (next === null) { break; }
+
+                node = next;
+            }
+        }
+        return next;
+    }
+
+    static anyNodeMatchesSelector(nodes, selector) {
+        const ELEMENT_NODE = Node.ELEMENT_NODE;
+        for (let node of nodes) {
+            for (; node !== null; node = node.parentNode) {
+                if (node.nodeType !== ELEMENT_NODE) { continue; }
+                if (node.matches(selector)) { return true; }
+                break;
+            }
+        }
+        return false;
+    }
 }
diff --git a/ext/mixed/js/text-scanner.js b/ext/mixed/js/text-scanner.js
index b8688b08..fb275452 100644
--- a/ext/mixed/js/text-scanner.js
+++ b/ext/mixed/js/text-scanner.js
@@ -17,7 +17,6 @@
 
 /* global
  * DOM
- * TextSourceRange
  * docRangeFromPoint
  */
 
@@ -119,20 +118,20 @@ class TextScanner extends EventDispatcher {
         }
     }
 
-    getTextSourceContent(textSource, length) {
+    getTextSourceContent(textSource, length, layoutAwareScan) {
         const clonedTextSource = textSource.clone();
 
-        clonedTextSource.setEndOffset(length);
+        clonedTextSource.setEndOffset(length, layoutAwareScan);
 
         if (this._ignoreNodes !== null && clonedTextSource.range) {
             length = clonedTextSource.text().length;
             while (clonedTextSource.range && length > 0) {
-                const nodes = TextSourceRange.getNodesInRange(clonedTextSource.range);
-                if (!TextSourceRange.anyNodeMatchesSelector(nodes, this._ignoreNodes)) {
+                const nodes = DOM.getNodesInRange(clonedTextSource.range);
+                if (!DOM.anyNodeMatchesSelector(nodes, this._ignoreNodes)) {
                     break;
                 }
                 --length;
-                clonedTextSource.setEndOffset(length);
+                clonedTextSource.setEndOffset(length, layoutAwareScan);
             }
         }
 
diff --git a/test/test-document.js b/test/test-document.js
index 0d9026db..ba7acc49 100644
--- a/test/test-document.js
+++ b/test/test-document.js
@@ -94,10 +94,12 @@ async function testDocument1() {
     const vm = new VM({document, window, Range, Node});
     vm.execute([
         'mixed/js/dom.js',
+        'fg/js/dom-text-scanner.js',
         'fg/js/source.js',
         'fg/js/document.js'
     ]);
-    const [TextSourceRange, TextSourceElement, docRangeFromPoint, docSentenceExtract] = vm.get([
+    const [DOMTextScanner, TextSourceRange, TextSourceElement, docRangeFromPoint, docSentenceExtract] = vm.get([
+        'DOMTextScanner',
         'TextSourceRange',
         'TextSourceElement',
         'docRangeFromPoint',
@@ -106,7 +108,7 @@ async function testDocument1() {
 
     try {
         await testDocumentTextScanningFunctions(dom, {docRangeFromPoint, docSentenceExtract, TextSourceRange, TextSourceElement});
-        await testTextSourceRangeSeekFunctions(dom, {TextSourceRange});
+        await testTextSourceRangeSeekFunctions(dom, {DOMTextScanner});
     } finally {
         window.close();
     }
@@ -179,7 +181,7 @@ async function testDocumentTextScanningFunctions(dom, {docRangeFromPoint, docSen
         if (source === null) { continue; }
 
         // Test docSentenceExtract
-        const sentenceActual = docSentenceExtract(source, sentenceExtent).text;
+        const sentenceActual = docSentenceExtract(source, sentenceExtent, false).text;
         assert.strictEqual(sentenceActual, sentence);
 
         // Clean
@@ -187,7 +189,7 @@ async function testDocumentTextScanningFunctions(dom, {docRangeFromPoint, docSen
     }
 }
 
-async function testTextSourceRangeSeekFunctions(dom, {TextSourceRange}) {
+async function testTextSourceRangeSeekFunctions(dom, {DOMTextScanner}) {
     const document = dom.window.document;
 
     for (const testElement of document.querySelectorAll('.test[data-test-type=text-source-range-seek]')) {
@@ -220,8 +222,8 @@ async function testTextSourceRangeSeekFunctions(dom, {TextSourceRange}) {
 
         const {node, offset, content} = (
             seekDirection === 'forward' ?
-            TextSourceRange.seekForward(seekNode, seekOffset, seekLength) :
-            TextSourceRange.seekBackward(seekNode, seekOffset, seekLength)
+            new DOMTextScanner(seekNode, seekOffset, true, false).seek(seekLength) :
+            new DOMTextScanner(seekNode, seekOffset, true, false).seek(-seekLength)
         );
 
         assert.strictEqual(node, expectedResultNode);