Oh, one have to hover over the function name to see, that's a link! Maybe I have to blame my monitor because of the more grayish then bluish color.

According to documentation,  the tformat paramer 5 is ignored:

"Specify time in the form "hh:mm:ss+/-hh:mm" (24-hour clock). The time is specified as local time. The following optional suffix may be supplied, but is ignored: a plus (+) or minus (–) suffix followed by the offset of local time from Coordinated Universal Time (UTC). A minus sign (-hh:mm) indicates that the local time is earlier (westward) of the Greenwich meridian by the returned offset number of hours and minutes. A plus sign (+hh:mm) indicates that the local time is later (eastward) of the Greenwich meridian by the returned offset number of hours and minutes."

The same goes for the parameter values 6, 7 and 8

write $zdth("2021-11-04T11:10:00+0100",3,5)  --> 66052,40200
write $zdth("2021-11-04T11:10:00+0200",3,5)  --> 66052,40200
write $zdth("2021-11-04T11:10:00-0100",3,5)  --> 66052,40200

That part of the question was "out of my viewport". Yes, that's an important point.

You asked for "cached routines"... the above clear buffer function, as far, as I know, resets the global buffers only, not the routine buffers. Just for completeness. Maybe someone with a more detailed knowledge could me agree or disagre...

The question was (see the original post),  why does a command work in a terminal but not in a method. And, as you know, the answer lies in the scoping. I would say, he (@David Hockenbroch) tries to learn and understand the nature of indirection and is not working on a production grade problem.

But maybe I'm wrong... who knows.

He (@David Hockenbroch) is playing with inderection, using $classmethod() instead of ##class(classname).methodname(...)  does not solve the scoping problem:

ClassMethod testvalidator(class As %String, value As %String) As %Status
{  
  set validator = "sc = $classmethod(class, ""IsValid"", value)"
   write validator,!
   set @validator
   write sc,!
   quit sc
}

The above method gives you the same <UNDEF> error because of non global scoping! By using indirection both variables (validator and sc) must have global scope.

As @Sergei Shutov pointed out, you can switch off the procdere block by a keyword for the whole class. Additionaly, you can switch on or off the procedure block keyword for a particular  method too. In your case:

class Some.Class  Extends %RegisteredObject
{
/// a procedure block method
ClassMethod ProcBlock()
{
}

/// a nonprocedurblock method
ClassMethod NoProcBlock() [ ProcedureBlock = 0 ]
{
// Caution: All variables have a global scope, hence, they will overwrite variables with the same name, which were created previously. To avoid this, use the NEW command, to protect them (if desired).
}

}

According to the task, "...You will receive an integer number and you will return a new number..."

set s=9999999999999999999
write s --> 10000000000000000000
write AddWater(s) --> 1  // which is the expected result

The above method works also for cases, where s contains a string of digits

set a="9999999999999999999"
write a  --> 9999999999999999999
set res=AddWater(s)
write res ---> 999...<165 more nines>...999
write $length(s) --> 19
write $length(res) --> 171  // 19 * 9 = 171

So why do you show those devils?

Oh, I see right now, we can save one byte...

ClassMethod AddWater(s)
{
   f i=$l(s):-1:1 s t=$e(s,i),$e(s,i)=10**t-1/9*t
   q $tr(s,0)
}

%FromJSON is not a class, it's a method of %DynamicObject and is available in IRIS and for Cache  version 2016.2 and later.

If you create a class, you can it declare as a hidden class, see

https://docs.intersystems.com/iris20211/csp/docbook/DocBook.UI.Page.cls…

Class My.Class Extends What.Ever [ Hidden ]
{
}

will be a hidden class.  

For your own classes you can adjust this class keyword as you like but for the system classes - there is no chance, they lie somwhere on ISC servers (and, but this is my very own opinion, not very wise. First, I would like to read the documentation for the version I have installed (and not always the latest version) and second, I would like to read the doc everywhere! For example, I have a 10 hour flight, and want to work. And in case, a server only has a  local LAN access, then you have no docu!).

you wrote in your original message, I quote "...But if I add one additional column such as below the query fails:" and now, see above, you talk about "batch term session".

I'm confused.

Of course, my loop is a little bit too short ;-(  the correct one is

ClassMethod Merge(obj...) {
   set res=obj(1)
   do res.%Remove("NextCursor")
   for i=2:1:obj {
      for j=0:1:obj(i).OptOuts.%Size()-1 do res.OptOuts.%Push(obj(i).OptOuts.%Get(j))
   }
   quit res
}

 Sorry, it seems, a telephone call and writing  does not go together.

For the LAST() function you can also use just an expression:

LAST(y,m)  QUIT $ZDATEH(m=12+y*100+(m#12)+1*100+1,8)-1

<Nitpicking OFF>

By the way, if you are just interested, how many days a month in a given year has, there is a simple formula:

LastDay(y,m)  quit $s(m-2:m\8+m#2+30, 1:y#4=0+28)

In the above formula, it's OK to use short leap year calculation (y#4=0) for contemporary dates (date from 1901 until 2099) else case you have to stick to the long format: (y#4=0)-(y#100=0)+(y#400=0)

As we know, an email can contain one or more attached email(s), which in turn can contain other attached mails ... so we have to work recursively until the end. The following program excerpt should show the concept:

ClassMethod GetMails(popAddr, popUser, popPass)
{
   set pop=##class(%Net.POP3).%New(), cnt=0
   if pop.Connect(popAddr, popUser, popPass) {
      if pop.GetMailBoxStatus(.cnt,.siz) {
         for id=1:1:cnt {
            if pop.Fetch(id,.msg,0) do ..getParts(pop,msg,id,0)
         }
      }
   }
}

ClassMethod getParts(pop, msg, id, lev)
{
   for i=1:1:msg.Parts.Count() {
      set part=msg.Parts.GetAt(i)
      set typ=$zcvt(part.CntentType,"l")
      set dsp=part.Headers.GetAt("content-disposition")
      
      if typ["message/rfc822" {
         // this is another email, we step one level deeper
         if pop.GetAttachedEmail(msg.Parts.GetAt(i), .new) do ..getParts(pop, new, id, lev+1)
         
      } elseif dsp["attachment" {
         // attachments
         if typ["application/pdf" {
         } elseif typ["image" {
         } elseif ... {
         }
      } elseif typ["text" {
      } elseif ... {
      }
   }
}