added discussion of: PROPOSED optional timestamp for output

org-babel.org

@@ -203,6 +203,23 @@ would then be [[#sandbox][the sandbox]].
 ** PROPOSED optional timestamp for output
    Add option to place an (inactive) timestamp at the #+resname, to
    record when that output was generated.
+
+*** source code block timestamps (optional addition)
+    If we did this would we then want to place a timestamp on the
+    source-code block, so that we would know if the results are
+    current or out of date?  This would have the effect of caching the
+    results of calculations and then only re-running if the
+    source-code has changed.  For the caching to work we would need to
+    check not only the timestamp on a source-code block, but also the
+    timestamps of any tables or source-code blocks referenced by the
+    original source-code block.
+
+**** maintaining source-code block timestamps
+     It may make sense to add a hook to `org-edit-special' which could
+     update the source-code blocks timestamp.  If the user edits the
+     contents of a source-code block directly I can think of no
+     efficient way of maintaining the timestamp.
+
 ** PROPOSED use example block for large amounts of stdout output?
    We're currently `examplizing' with : at the beginning of the line,
    but should larger amounts of output be in a