Please assist: I wrote the following code in the Catalog.Contractors.ListForm:
&AtClient
Procedure DescriptionOnChange(Item)
   If Object.FullDescription = "" Then
       Object.FullDescription = Object.FullDescription;
   EndIf;
EndProcedure
It produced the following error message:
{ Catalog.Contractors.Form.ListForm.Form (4,8)}: Variable is not defined (Object)
<<?>>If Object.FullDescription = "" Then (Verification: Thin Client)
But if I’m doing the same for the Catalog.Contractors.ItemForm, it works just fine!

This is because there is no Object form attribute for the ListForm. There is a List attribute which contains not a single object as in ItemForm, but a list of them.

Thank you! That was helpful!