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diff --git a/ext/js/general/regex-util.js b/ext/js/general/regex-util.js
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+/*
+ * Copyright (C) 2021  Yomichan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/**
+ * This class provides some general utility functions for regular expressions.
+ */
+class RegexUtil {
+    /**
+     * Applies string.replace using a regular expression and replacement string as arguments.
+     * A source map of the changes is also maintained.
+     * @param text A string of the text to replace.
+     * @param sourceMap An instance of `TextSourceMap` which corresponds to `text`.
+     * @param pattern A regular expression to use as the replacement.
+     * @param replacement A replacement string that follows the format of the standard
+     *   JavaScript regular expression replacement string.
+     * @return A new string with the pattern replacements applied and the source map updated.
+     */
+    static applyTextReplacement(text, sourceMap, pattern, replacement) {
+        const isGlobal = pattern.global;
+        if (isGlobal) { pattern.lastIndex = 0; }
+        for (let loop = true; loop; loop = isGlobal) {
+            const match = pattern.exec(text);
+            if (match === null) { break; }
+
+            const matchText = match[0];
+            const index = match.index;
+            const actualReplacement = this.applyMatchReplacement(replacement, match);
+            const actualReplacementLength = actualReplacement.length;
+            const delta = actualReplacementLength - (matchText.length > 0 ? matchText.length : -1);
+
+            text = `${text.substring(0, index)}${actualReplacement}${text.substring(index + matchText.length)}`;
+            pattern.lastIndex += delta;
+
+            if (actualReplacementLength > 0) {
+                sourceMap.insert(index, ...(new Array(actualReplacementLength).fill(0)));
+                sourceMap.combine(index - 1 + actualReplacementLength, matchText.length);
+            } else {
+                sourceMap.combine(index, matchText.length);
+            }
+        }
+        return text;
+    }
+
+    /**
+     * Applies the replacement string for a given regular expression match.
+     * @param replacement The replacement string that follows the format of the standard
+     *   JavaScript regular expression replacement string.
+     * @param match A match object returned from RegExp.match.
+     * @return A new string with the pattern replacement applied.
+     */
+    static applyMatchReplacement(replacement, match) {
+        const pattern = this._matchReplacementPattern;
+        pattern.lastIndex = 0;
+        return replacement.replace(pattern, (g0, g1, g2) => {
+            if (typeof g1 !== 'undefined') {
+                const matchIndex = Number.parseInt(g1, 10);
+                if (matchIndex >= 1 && matchIndex <= match.length) {
+                    return match[matchIndex];
+                }
+            } else if (typeof g2 !== 'undefined') {
+                const {groups} = match;
+                if (typeof groups === 'object' && groups !== null && Object.prototype.hasOwnProperty.call(groups, g2)) {
+                    return groups[g2];
+                }
+            } else {
+                switch (g0) {
+                    case '$': return '$';
+                    case '&': return match[0];
+                    case '`': return replacement.substring(0, match.index);
+                    case '\'': return replacement.substring(match.index + g0.length);
+                }
+            }
+            return g0;
+        });
+    }
+}
+
+// eslint-disable-next-line no-underscore-dangle
+RegexUtil._matchReplacementPattern = /\$(?:\$|&|`|'|(\d\d?)|<([^>]*)>)/g;