Fix highlighting

app/SearchDisplace/SearchAndDisplace.php

@@ -60,16 +60,16 @@ class SearchAndDisplace
         $updatedDocumentContent = '';
         $currentIndex = 0;
 
-        foreach ($searchers as $start => $searcherItem) {
+        foreach ($searchers as $s => $searcherItem) {
             $partialContent = substr($this->documentContent, $currentIndex, $searcherItem['start'] - $currentIndex);
 
             $updatedDocumentContent = $updatedDocumentContent . $partialContent;
 
-            $start = strlen($updatedDocumentContent);
+            $start = mb_strlen($updatedDocumentContent);
 
             $updatedDocumentContent = $updatedDocumentContent . $replacements[$searcherItem['searcher']];
 
-            $end = strlen($updatedDocumentContent) - 1;
+            $end = mb_strlen($updatedDocumentContent) - 1;
 
             if ($start <= $end) {
                 $replacementIndexes[$searcherItem['searcher']][] = [