anchor.diff:  String datetime = 'custom y 1983 m 10 d 13 22:15:30 Z';
   DateTimeFormatter dtf = DateTimeFormatter.ofPattern(
           "'custom' 'y' yyyy 'm' MM 'd' dd HH:mm:ss VV");
  -ZonedDateTime zdt = ZonedDateTime.parse(datetime, dtf);
  -----
  -Note the use of a custom DateTimeFormatter.
  +ZonedDateTime zdt = ZonedDateTime.parse(datetime, dtf); <1>
  +----
  +<1> Note the use of a custom DateTimeFormatter.
   
   ===== Datetime Formatting Examples
   
  
positive.code:     // handle condition
  }
  ----
  
negative.code: <<painless-api-reference-shared-ChronoUnit, ChronoUnit>>
  to calculate the difference between two complex datetimes if supported.
  
  ===== Datetime Difference Examples
  
  * Difference in milliseconds between two numeric datetimes
  +
  