code: func ParseQuery(query string) (CertificateFilter, error) {
  	parts := strings.SplitN(query, ":", 2)
  	if len(parts) != 2 {
  		return nil, errors.New("info: expected a query in the form type:regexp")
  	}
  
  	// parts[0]: type
  	// parts[1]: regexp
  	f, ok := filters[parts[0]]
  	if !ok {
  		return nil, errors.New("info: unknown filter type " + parts[0])
  	}
  
  	return f(parts[1])
  }
docs: // ParseQuery attempts to parse a query in the form "type:regexp",
  // returning a filter if successful.