code: func (t *Filter) Allow(e *Entry) bool {
  	if e == nil {
  		return true
  	}
  	if e.Level > t.MaxLevel {
  		return false
  	}
  	if t.catNames[e.Category] {
  		return true
  	}
  	for _, cat := range t.catPrefixes {
  		if strings.HasPrefix(e.Category, cat) {
  			return true
  		}
  	}
  	return len(t.catNames) == 0 && len(t.catPrefixes) == 0
  }
docs: // Allow checks if a message meets the severity level and category requirements.