These are more complicated commands that don't do anything by themselves. Instead, they provide conditions for when other events happen.
It's extremely common to have some actions in Storyboarding repeat themselves a fixed number of times. For instance, you may want to have an object to fade in and out constantly during a certain playtime. In this case, it would be best to use a loop.
Loops are done on commands within an object, not across several objects. They are treated as a special type of command of the form:
_L,(starttime),(loopcount) __(event),(easing),(relative_starttime),(relative_endtime),(params...) // More events allowed
Hence, a loop that fades in and out, taking a total of 1 second each time around, for 30 seconds total (therefore 30 loops), starting at time 60000:
Sprite,Pass,Centre,"Sample.png",320,240 _L,60000,30 __F,0,0,500,0,1 __F,0,500,1000,1,0
In addition to the "implicit" player feedback via the separate Pass/Fail layers, you can use one of several Trigger conditions to cause a series of events to happen whenever that condition is fulfilled within a certain time period. The official specification calls these "trigger loops" due to their syntactic similarity to Loops (L), but they aren't loops at all, so here they are simply called "Triggers".
Triggers take the form:
_T,(triggerType),(starttime),(endtime) __(event),(easing),(relative_starttime),(relative_endtime),(params...) // More events allowed
If a trigger condition occurs while another trigger is running, the earlier trigger is stopped, and the new trigger starts. Triggers will not occur until other commands are finished, so it's usually best to either use only triggers on an object declaration or not at all.
For instance, in Elite Beat Agents, typically top screen (a.k.a. the storyboard) will be covered in white for a split-second during a transition among states. We can do the same thing with a completely white 640x480 image, assuming a particular playable section is from 20000 to 40000:
Sprite,Foreground,Centre,"LargeWhiteImage.png",320,240 _T,Passing,20000,40000 __F,0,0,500,1 __F,0,500,501,0 _T,Failing,20000,40000 __F,0,0,500,1 __F,0,500,501,0