Another challenge is to enable WebSocket protocol on your webserver
I just had the "pleasure" to do this for IIS 👺
It's not a default

(error on compiling within a class) like: 
#define TestIf(%arr)        if (%arr > 0) { QUIT 5 }    ; no final dot.

#define is an element of ObjectScript
so it has to be embedded in a [Class]Method 
and it is only available within that method

It can't be flying free inside a class definition.

If you need your $$$TestIf(...)  in more than 1 method, you can deposit
it in some TestIf.INC  and include it BEFORE the Class statement !!
Then it is visible to ALL methods.

Attention: You can INCLUDE just 1 single  *.INC in a class definition.
If you need more than 1, you have to cascade it with #include  in  the first *.inc

Include TestIf

Class A.PERSON1 Extends %Library.Persistent
{
Parameter GlobalName = "^.........!"  ;;
/// .......
ClassMethod michael(param) as %Integer
{
    $$$TestIf(param)
 .........
    quit $$$OK
}

The AI example is misleading anyhow, as it just does a $O loop without any action to be done 
*.inc is typically kind of text generation code during compilation. 
What is your expectation for using the *.inc ?

%in and %gn are just text replacement parameters:
%gn is used as globalname, %in as first level subscript

If you just see pre you may have a problem with your  &html< ........>  sequence
that translates to write ........,! including all quoting requirements,

while <pre> any text </pre>  is just straight HTML

and  #(variable)# is a CSP instruction to display the actual content of a variable
and avoid any extra spaces

this may help to get the plain %request object:

k ^SPOOL s %io=$I O 2 u 2 ZW %request c 2 u %io

or whatever object you need to trace

YEAH, it's built for visual CSP pages

From Class Docs.:

Somewhere in the CSP page. This is just ~20% of the content

There are geographies in this world where a Decimal-Comma is used instead of a Decimal-Point.
Never met a Decimal-Pipe  😉 

Just received notice:

Provide a single page view of free space in IRIS DBs
has changed status to: Community Opportunity

Just to verify.

Status is:  "NEEDS REVIEW" for almost a month!  
I have a feeling.

I miss 4 points for the community idea for my Snapshot:
https://ideas.intersystems.com/ideas/DPI-I-799
It's also filled into OEX

To me, the most impressive fact about InterSystems is that it doesn't
hide or deny its roots or reject its history, and keep its backward compatibility.

I remember a customer who had composed and used an incredible complicated
program to create knitwear patterns with his equipment for over 30 years without change.
When he migrated to IRIS it was running perfectly without changing a single bit.

This still impresses me more than all the new language features
that force me to adjust versions as an ongoing challenge.

3 variants come to my mind

1. writing to ErrorLog  Do LOG^%ETN()
2.  write to Systrem message.log

    set %evgeny=$io
    open 1 use 1 write !,"Was in my REST code",! close 1
    use %evgeny

3. If you have a terminal session  LOCK  ^%EVGENY --- And into your code, add this simple loop 

4.  for  LOCK +^%EVGENY QUIT:$TEST   HANG 0.5

   Now your method loops, and you can attach with any external debugger. Releasing the LOCK from Terminal does the "un-freeze"

Simplified:  %CSP.Page is a collection of methods and event handlers without any own properties.
Related data are kept outside in %CSP.Request and %CSP.response.
But you may mimic InitialExpressions by using PARAMETERS 

Not really surprised. The Python version was in as the first anyhow

I understand that using the IRIS Native API is the important feature.
Is this also valid for IRIS Native API for ObjectScript ????.  
No doubt it is EXTERNAL on a different instance,
talking to the same interface as Java, NodeJS, Python, .NET
facing the same limitations  (Functions !)