When generating cache-keys for rendered content in web applications, you have to take into account all variables that might change the result.
In dynamic environments like rails these can be defined in different places: the controller, a model, the session or the server environment. And they can be referenced in the template, in a template rendered within the template or a helper.
Can you think of a way to automatically generate a list of variables that contribute to the content of the rendered template, maybe using ParseTree?