code: public static Expression clockStr(String format) {
          if (format == null || format.isEmpty()) {
              return x("CLOCK_STR()");
          }
          return x("CLOCK_STR(\"" + format + "\")");
      }
docs: Returned expression results in system clock at function evaluation time, as a string in a supported format.
  Varies during a query. Supported formats:
  
  - "2006-01-02T15:04:05.999Z07:00": Default format. (ISO8601 / RFC3339)
  - "2006-01-02T15:04:05Z07:00" (ISO8601 / RFC3339)
  - "2006-01-02T15:04:05.999"
  - "2006-01-02T15:04:05"
  - "2006-01-02 15:04:05.999Z07:00"
  - "2006-01-02 15:04:05Z07:00"
  - "2006-01-02 15:04:05.999"
  - "2006-01-02 15:04:05"
  - "2006-01-02"
  - "15:04:05.999Z07:00"
  - "15:04:05Z07:00"
  - "15:04:05.999"
  - "15:04:05"