Thanks that is what the vibe i got and what AI leant towards. 

I see now it is baked in this tIsLookup bascially saying it needs to be in the Ens Rule function set or Util function set and it's called Lookup or for the exists function. It is no problem it was just an ask if missed something, can always select the standard one if need the lookup dropdown then write v2 afterwards. 

Set tIsLookup = ((tClassName = "Ens.Rule.FunctionSet") || (tClassName = "Ens.Util.FunctionSet")) && ((tFunctionName = "Lookup") || (tFunctionName = "Exists"))

Thanks this looks right and indeed i think a correct answer for use in other classes. 

I gave this a go pretty much (less elegantly)

SELECT List(distinct TableName) FROM Ens_Util.LookupTable

Parameter SETTINGS = "LookupTableName:selector?context={MyApp.Utils.LookupHelper.GetLookupTableNames}";
Property LookupTableName As %String;

In my case like Julian says think it's baked into the zen page within the dtl editor

Also saving passwords has led to somewhere a password getting cached and kept locking out my AD account dispite updating them all and had to reset studio extension completely so don't want to save passwords