Just leave them blank after the '=' character, so that user does not need to manually delete or over-write if they want to do sub-sampling (where its not required to fill in these, as auto wil lbe applied to the subsampling irrespective of these variables)
Just leave them blank after the '=' character, so that user does not need to manually delete or over-write if they want to do sub-sampling (where its not required to fill in these, as auto wil lbe applied to the subsampling irrespective of these variables)