Many thanks for your reply

My registered function in xl returns a string but inbetween it has access to the active sheet/active cell and attempts to create a dropdown combo containing a set of values, using the Validation object much in the same way the following vba code would do

Function GetSomeData() as strin

dim str as strin
' do some work to populate the strin

ActiveCell.Selec
ActiveCell.Clea
With Selection.Validatio
.Delet
.Add Type:=xlValidateList, AlertStyle:=xlValidAlertStop, Operator:=xlBetween, Formula1:=str
.IgnoreBlank = Tru
.InCellDropdown = Tru
.InputTitle = "
.ErrorTitle = "
.InputMessage = "
.ErrorMessage = "
.ShowInput = Fals
.ShowError = Tru
End Wit
GetSomeData = GetFirstString(str) '
End Function