underrun action

On the wiki page of mAirlist 4.0 I’ve read:

[size=8pt]Likewise, if there is a gap before a fixed time item (or a backtimed chain) - a so-called underrun - a warning will be displayed along with the item. When the automation reaches the item before the scheduled time, you can instruct the automation to wait (that is, play a silence element that is automatically inserted) until the time is reached. This option can be set separately for soft and fixed timed items.[/size]

Can somebody explain how to do this?

kind regards,

mAirListConfig -> Playlist -> Options

Thanks Torben!