Derived Field - What does "Groups" do?

[CP1]

I am trying to understand the sample script in the "Derived fields" (Link).

Calendar:
DECLARE FIELD DEFINITION TAGGED '$date'
   Parameters
      first_month_of_year = 1
   Fields
      Year($1) As Year Tagged ('$numeric'),
      Month($1) as Month Tagged ('$numeric'),
      Date($1) as Date Tagged ('$date'),
      Week($1) as Week Tagged ('$numeric'),
      Weekday($1) as Weekday Tagged ('$numeric'),
      DayNumberOfYear($1, first_month_of_year) as DayNumberOfYear Tagged ('$numeric')
   Groups 
      Year, Week, Weekday type drilldown as YearWeekDayName, 
      Year, Month, Date type collection as YearMonthDate;

Could not find any document that explain what the "Groups" does.

I am looking at doing drilldown with the date field, so I want to understand the code on the "Groups" as "YearWeekDayName" seems to type as a drilldown.

Thanks.

[Ralf-Narfeldt · Accepted solution]

Groups are currently not supported when declaring field definitions, as is seen in the syntax of the Declare help topic.
https://help.qlik.com/en-US/sense/June2019/Subsystems/Hub/Content/Sense_Hub/Scripting/ScriptRegularS...

The inclusion of groups in the example is a mistake that we will correct in the next update of the help.

Thank you for bringing this to our attention, and apologies for the inconvenience.