Programmatically added event handler name should match pattern: Attachable_ prefix
// Parameters:
// Item - FormField
Procedure Incorrect(Item)
Item.SetAction("OnChange", "IncorrectOnChange");
EndProcedure
// Parameters:
// Item - FormField
Procedure Correct(Item)
Item.SetAction("OnChange", "Attachable_CorrectOnChange");
EndProcedure