def timestamp_insert(sender, frames):
        """
        Timestamp the created and modified fields for all documents. This method
        should be bound to a frame class like so:

        ```
        MyFrameClass.listen('insert', MyFrameClass.timestamp_insert)
        ```
        """
        for frame in frames:
            timestamp = datetime.now(timezone.utc)
            frame.created = timestamp
            frame.modified = timestamp