What is meant by 'Tandem Repeats' and 'Mask Tandems' when using the RealTimeDesign™ software?

The 'Custom Mode' of the RealTimeDesign™ (RTD™) software will identify strings of a single base and short simple repeats within the input sequence. These features called ‘Tandem Repeats’ are automatically masked and avoided during assay design by converting the repeat bases into strings of N’s. By using Custom Mode the user may choose to unmask some or all of these repeat sequences and make them available for placement of the probes and primers. To unmask repeat sequences, expand the 'Features' window by clicking on the box for 'TandemRepeats' and select 'Unmask All' or choose specific tandem repeats to unmask.