I was able to get this working, at least the example above attaching to Released Production Orders (which was quite helpful as this is one of the pages that I needed attachments on).

All the quotation marks in the examples are wrong. This is probably from the web page re-writting them to fancy quotes or something.
There are line breaks also that need to be removed.

** in launch.json, set “startupObjectId”: 99000831,
** Not stated in instructions: You need to add IWX dependencies to app.json

“dependencies”: [
{
“id”: “d50afbbf-aff3-4dac-bce7-8686b375b994”,
“name”: “DocXtender”,
“publisher”: “Insight Works”,
“version”: “2.1.8635.2”
}
],

Here is copy/paste of my working code. It may break also when the page renders it, but it works.

namespace MHW.DocXtender;

using Microsoft.Manufacturing.Document;
using Microsoft.Foundation.Attachment;

pageextension 50106 “IWX Released Prod. Order” extends “Released Production Order”
{
layout
{
addfirst(factboxes)
{
part(“IWX Attached Documents”; “Document Attachment Factbox”)
{
ApplicationArea = All;
Caption = ‘Attachments’;
SubPageLink = “Table ID” = const(5405),
“No.” = field(“No.”);
}
}
}
}

codeunit 50106 “IWX codeunit”
{
EventSubscriberInstance = StaticAutomatic;

[EventSubscriber(ObjectType::Codeunit, Codeunit::”IWX DocXtender”, ‘OnGetCustomRecRefFromDocAttachment’, ”, false, false)]
local procedure OnGetCustomRecRefFromDocAttachmentDocXtender(precDocumentAttachment: Record “Document Attachment”; var prrRecordRef: RecordRef; var lbRecordRefHandled: Boolean);
var
lrecProductionOrder: Record “Production Order”;
begin
// Set the table for the custom record, when attached documents using drag-and-drop with DocXtender
if not lbRecordRefHandled then begin
case precDocumentAttachment.”Table ID” of
Database::”Production Order”:
begin
prrRecordRef.Open(Database::”Production Order”);
if lrecProductionOrder.Get(lrecProductionOrder.Status::Released,
precDocumentAttachment.”No.”) then begin
prrRecordRef.GetTable(lrecProductionOrder);
lbRecordRefHandled := true;
end;
end;
end;
end;
end;

[EventSubscriber(ObjectType::Codeunit, Codeunit::”IWX DocXtender”, ‘OnAfterOpenForRecRef’, ”, false, false)]
local procedure OnAfterOpenForRecRefDocXtender(var precDocumentAttachment: Record “Document Attachment”; var prrRecordRef: RecordRef);
var
lfrFieldRef: FieldRef;
lcodRecNo: Code[20];
begin
// Set filter for custom record when opening document attachment details
case prrRecordRef.Number of
Database::”Production Order”:
begin

lfrFieldRef := prrRecordRef.Field(2);
lcodRecNo := lfrFieldRef.Value;
precDocumentAttachment.SetRange(“No.”, lcodRecNo);
precDocumentAttachment.SetRange(“Line No.”, 0);
end;
end;
end;

[EventSubscriber(ObjectType::Page, Page::”Document Attachment Details”, ‘OnAfterOpenForRecRef’, ”, false, false)]
local procedure OnAfterOpenForRecRef(var DocumentAttachment: Record “Document Attachment”; var RecRef: RecordRef);
var
lfrFieldRef: FieldRef;
lcodRecNo: Code[20];
begin
// Set filter for custom record when opening document attachment details
case RecRef.Number of
Database::”Production Order”:
begin
lfrFieldRef := RecRef.Field(2);
lcodRecNo := lfrFieldRef.Value;
DocumentAttachment.SetRange(“No.”, lcodRecNo);
DocumentAttachment.SetRange(“Line No.”, 0);
end;
end;
end;

[EventSubscriber(ObjectType::Page, Page::”Document Attachment Factbox”, ‘OnBeforeDrillDown’, ”, false, false)]
local procedure OnBeforeDrillDown(DocumentAttachment: Record “Document Attachment”; var RecRef: RecordRef);
var
lrecProductionOrder: Record “Production Order”;
begin
// Set the table for the custom record, when attaching documents manually
case DocumentAttachment.”Table ID” of
Database::”Production Order”:
begin
RecRef.Open(Database::”Production Order”);
if lrecProductionOrder.Get(lrecProductionOrder.Status::Released, DocumentAttachment.”No.”) then
RecRef.GetTable(lrecProductionOrder);
end;
end;
end;
}