Add an example of keeping a history of previously cached response versions

docs/examples.md

diff --git a/docs/examples.md b/docs/examples.md
index d193680..e9cb3ce 100644
--- a/docs/examples.md
+++ b/docs/examples.md
@@ -202,6 +202,23 @@
 
 :::
 
+### Response history
+```{include} ../examples/history.py
+:start-line: 2
+:end-line: 3
+```
+
+:::{dropdown} Example
+:animate: fade-in-slide-down
+:color: primary
+:icon: file-code
+
+[benchmark.py](https://github.com/requests-cache/requests-cache/blob/main/examples/history.py)
+```{literalinclude} ../examples/history.py
+:lines: 5-
+```
+:::
+
 ### Using with GitHub Actions
 This example shows how to use requests-cache with [GitHub Actions](https://docs.github.com/en/actions).
 Key points:

examples/history.py

diff --git a/examples/history.py b/examples/history.py
new file mode 100644
index 0000000..fb99e3d
--- /dev/null
+++ b/examples/history.py
@@ -0,0 +1,42 @@
+#!/usr/bin/env python3
+"""
+An example of keeping a history of cached responses, for later comparison or analysis
+"""
+from time import sleep
+
+from requests_cache import CachedSession
+
+
+class CachedHistorySession(CachedSession):
+    """A CachedSession that keeps a copy of all previously cached responses"""
+
+    def send(self, *args, **kwargs):
+        """Save a copy of every new response"""
+        response = super().send(*args, **kwargs)
+        if not response.from_cache:
+            self.cache.save_response(response, f'{response.cache_key}_{response.created_at}')
+        return response
+
+    def get_response_history(self, response):
+        """Get a history of previously cached versions of the given response"""
+        return [
+            self.cache.responses[k]
+            for k in self.cache.responses.keys()
+            if k.startswith(response.cache_key) and k != response.cache_key
+        ]
+
+
+def demo():
+    session = CachedHistorySession(expire_after=1)
+    n_history_items = 3
+    for i in range(n_history_items):
+        response = session.get('https://httpbin.org/get')
+        if i < n_history_items - 1:
+            sleep(1)
+
+    for r in session.get_response_history(response):
+        print(r)
+
+
+if __name__ == '__main__':
+    demo()