code: def Add(self, category, label, age):
      
      now = rdfvalue.RDFDatetime.Now()
      category = utils.SmartUnicode(category)
  
      for active_time in self.active_days:
        self.categories[active_time].setdefault(label, {})
        if (now - age).seconds < active_time * 24 * 60 * 60:
          self.categories[active_time][label][
              category] = self.categories[active_time][label].get(category, 0) + 1
docs: Adds another instance of this category into the active_days counter.
  
      We automatically count the event towards all relevant active_days. For
      example, if the category "Windows" was seen 8 days ago it will be counted
      towards the 30 day active, 14 day active but not against the 7 and 1 day
      actives.
  
      Args:
        category: The category name to account this instance against.
        label: Client label to which this should be applied.
        age: When this instance occurred.