diff --git a/src/xslt.h b/src/xslt.h
--- a/src/xslt.h
+++ b/src/xslt.h
@@ -14,6 +14,13 @@
 QByteArray fromUnicode(const QString &data);
 void replaceCharsetHeader(QString &output);
 
+/**
+ * Extract the content of a single file from the content string
+ * generated by the transformation scripts.
+ * @since 5.32
+ */
+QByteArray extractFileToBuffer(const QString &content, const QString &filename);
+
 bool saveToCache(const QString &contents, const QString &filename);
 
 void setupStandardDirs(const QString &srcdir = QString());
diff --git a/src/xslt.cpp b/src/xslt.cpp
--- a/src/xslt.cpp
+++ b/src/xslt.cpp
@@ -358,6 +358,21 @@
 #endif
 }
 
+QByteArray extractFileToBuffer(const QString &content, const QString &filename)
+{
+    int index = content.indexOf(QStringLiteral("<FILENAME filename=\"%1\"").arg(filename));
+    if (index == -1) {
+        if (filename == QLatin1String("index.html")) {
+            return fromUnicode(content);
+        } else {
+            return QByteArray(); // null value, not just empty
+        }
+    }
+    QString data_file = splitOut(content, index);
+    replaceCharsetHeader(data_file);
+    return fromUnicode(data_file);
+}
+
 class DtdStandardDirs
 {
 public: