Thanks for the great article Sebastian!
I tried this myself for an Encounter property, and Step 4 can require a good bit of practice and digging through the frame-source HTML and the ^CacheTemp.HS.ViewerStreamlet global to really understand how it all works. Grabbing the streamletID for an Encounter requires some different code than grabbing the streamletID for an Allergy. For my use case the code for Step 4 was something like:

ClassMethod GetTransferredFromEDViewerTransform(patientID, episodeID) As %String
{
  set agkey= $g(^CacheTemp.HS.ViewerStreamlet("HSACCESS","P",patientID))
  set streamletID= $g(^CacheTemp.HS.ViewerStreamlet("HSACCESS","V",agkey,"ENC",episodeID))  
  set obj=##class(HS.SDA3.Streamlet.Encounter).%OpenId(streamletID)
  set encounterSDA3=##class(HS.SDA3.Encounter).%New()
  set st=encounterSDA3.XMLImportSDAString(obj.SDAString)
  set fromED=encounterSDA3.TransferredFromED
  
  if (fromED = 1) return "yes"
  return "no"
}

and the expression for Step 5 was something like:
set val=##class(Test.Viewer.Transforms).GetTransferredFromEDViewerTransform($g(rs.Data("PatientID")),$g(rs.Data("EpisodeID")))
 

Thank you Trent! This will come in handy the next time I need to investigate things like OAuth traffic

@Ben Spead, this is a great resource!
However, most of the links for online documentation, eLearning, and presentation slides no longer work in 2024. Would it be possible to update them?