can someone explain trigger.ids please

On a number of occasions now I have had mods fail to install . The debug file will say something like "unable to find trigger blahblah". I diligently go to IEDSP, look at triggers, find the entry for the appropriate trigger and add it to my trigger.ids file. But I really have no idea why this is, what trigger.ids does, and most importantly...why my copy is lacking dozens of lines that appear to be default? I just installed shadow magic mod and it required me to add these lines:

0x40E0 NextTriggerObject(O:Object*)
0x4102 HaveKnownSpellRES(S:Spell*)
0x40FE ClassLevelGT(O:Object*,I:Category*CLASSCAT,I:Value*)
0x40EA OriginalClass(O:Object*,I:Class*CLASS)
0x40E2 CheckSpellState(O:Object*,I:State*splstate)
0x40E6 IsWeaponRanged(O:Object*)
0x40F8 CanEquipRanged()
0x40EC WeaponEffectiveVs(O:Object*,I:Hand*HAND)
0x40F2 WeaponCanDamage(O:Object*,I:Hand*HAND)
0x40E7 ButtonDisabled(I:Button*BUTTON)


How were these not always there? I have most recent version of the game. Why do some mods require these lines but most don't. Mine now has 229 lines, what should it have?