let func =   
(StartDate as date, EndDate as date, optional Holidays as list, optional StartOfWeek as number) =>
let
    // optional StartOfWeek, if empty the week will start on Monaday
    startOfWeek = if StartOfWeek = null then 1 else StartOfWeek,

    // Get list of dates between Start- and EndDate
    ListOfDates = List.Dates(StartDate,Number.From(EndDate-StartDate),#duration(1,0,0,0)),

    // if the optional Holidays parameter is used: Keep only those dates in the list that don't occur in the list of Holidays;
    // otherwise continue with previous table
    DeleteHolidays = if Holidays = null then ListOfDates else List.Difference(ListOfDates, Holidays),

    // Select only the first 5 days of the week 
    // The 1 in the 2nd parameter of Date.DayOfWeek makes sure that Monday will be taken as first day of the week
    DeleteWeekends = List.Select(DeleteHolidays, each Date.DayOfWeek(_, startOfWeek) < 5 ),

    // Count the number of days (items in the list)
    CountDays = List.Count(DeleteWeekends)
in
    CountDays ,
documentation = [
Documentation.Name =  " Date.Networkdays.pq ",
Documentation.Description = " Returns the number of whole working days between StartDate and EndDate similar to the NETWORKDAYS-function in Excel. Working days exclude weekends and any dates identified in holidays. ",
Documentation.LongDescription = " Returns the number of whole working days between StartDate and EndDate similar to the NETWORKDAYS-function in Excel. Working days exclude weekends and any dates identified in (optional) holidays. ",
Documentation.Category = " Date ",
Documentation.Source = " www.TheBIccountant.com https://wp.me/p6lgsG-2fA .   ",
Documentation.Version = " 1.0 ",
Documentation.Author = " Imke Feldmann ",
Documentation.Examples = {[Description =  "  ",
Code = "  ",
Result = "  "]}]
  
 in  
  Value.ReplaceType(func, Value.ReplaceMetadata(Value.Type(func), documentation))