code: def annotate_event(ev, key, ts=None, namespace=None, **kwargs):
      
      ann = {}
      if ts is None:
          ts = time.time()
      ann["ts"] = ts
      ann["key"] = key
      if namespace is None and "HUMILIS_ENVIRONMENT" in os.environ:
          namespace = "{}:{}:{}".format(
              os.environ.get("HUMILIS_ENVIRONMENT"),
              os.environ.get("HUMILIS_LAYER"),
              os.environ.get("HUMILIS_STAGE"))
  
      if namespace is not None:
          ann["namespace"] = namespace
      ann.update(kwargs)
      _humilis = ev.get("_humilis", {})
      if not _humilis:
          ev["_humilis"] = {"annotation": [ann]}
      else:
          ev["_humilis"]["annotation"] = _humilis.get("annotation", [])
          # Clean up previous annotations with the same key
          delete_annotations(ev, key)
          ev["_humilis"]["annotation"].append(ann)
  
      return ev
docs: Add an annotation to an event.