Grass Valley NewsEdit XT v.5.5 - Manual (Page 152)

Chapter 7 Fine Tuning and Advanced Editing
150 Digital News Production
4. Enter a Duration for the filler and click OK .
The Timeline updates with the filler inserted into the sequence.
NOTE: You can also insert filler between Mark In and Mark Out
points on all tracks that are active. You cannot add a transition effect
between a clip and filler.