Search this forum for the CM_UDT_SVC class and the scripting.docx document (the doc can also be found in the KB).

These should get you started.

If it is just for reference, you should be able to add the UDT fields to a panel without a script.

Thanks for the reply Kevin. I did add the UDT, and UDF to the Sales Order Header. 

Now, after selection of the UDF, I also want to pop up other fields (also UDF) based on the selected item. Basically, pop up other attributes in the UDT of selected item.  Just like the sales order entry auto pops the Bill To and Ship To after user selects the customer.

Kevin, i don't recall ever seeing a UDT show up in that list, does it actually source the other fields of the record in the UDT based on the value selected in the UDF that uses the UDT for validation?

Thank you David. What is KB? 

Knowledgebase.

https://support.na.sage.com/selfservice/microsites/msbrowse.do?UMBrowseSelection=SG_SAGE100ERP_1

UDF_MY_DESCRIPTION is a field in my UDT.  It becomes available as a read only field (not copied into the transaction, just a display) with the UDT validation for an SO Header UDF.

Yes.

Well that's awesome, that leads me to believe the UDT is added as a child collection, good to know.

Think about TermsCode and the description (or Salesperson, Warehouse, ShipToCode, TaxSchedule...).  The transaction field is validated against the other table, so the related description is available for display on the panel through that link.  UDT validation seems to work the same way, creating a link to display related fields based on the selected value.