Fix Read the Docs build failure

_build/_sources/patterns/subclassing.rst.txt

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+Subclassing Flask
+=================
+
+The :class:`~flask.Flask` class is designed for subclassing.
+
+For example, you may want to override how request parameters are handled to preserve their order::
+
+    from flask import Flask, Request
+    from werkzeug.datastructures import ImmutableOrderedMultiDict
+    class MyRequest(Request):
+        """Request subclass to override request parameter storage"""
+        parameter_storage_class = ImmutableOrderedMultiDict
+    class MyFlask(Flask):
+        """Flask subclass using the custom request class"""
+        request_class = MyRequest
+
+This is the recommended approach for overriding or augmenting Flask's internal functionality.