More than one year ago, the Highborne were allowed to return the Night Elf society. The Highborne were originally exiled after the events of the Sundering, where Azeroth was split in two due to the Well of Eternity's destruction.
During this period, the Night Elves decreed it illegal to practice arcane magic, punishable by death. Furthermore, the offender's entire family would be publicly shamed over this event.
With the return of the Highborne, this ban was lifted in a way. The study of magic was permitted and the Highborne were allowed to return, but arcane magic is still forbidden on Teldrassil. The Highborne are still ostracized and treated somewhat poorly, though are protected from harm by the Temple. Even Shandris makes mention that it is only Tyrande's word keeping the Highborne safe.
Recent Night Elven students and apprentices to the Highborne have been showing up. The majority of these are younger elves, who came of age near the time of the Third War. Those who take up the arcane studies are usually met with confusion and misunderstanding from those around them.
There appears to be a rift in what Night Elves deem 'undead' and what they deem as 'spirits'. Spirits are phantasms while the undead are usually raised unnaturally by necromancy. Spirits seem to be pitied and should be destroyed to be given peace.
Corporeal undead, specifically The Scourge, has been referred to in a number of ways; Evil, miserable, and 'a direct affront to nature'. Furthermore, Elune's power, through the moonwells can actively destroy undead corruption and items.
The first encounter with necromancy the Night Elves had was in the War of the Ancients. Dreadlords were capable of raising the dead elves to fight for them.
As fel magic is an extension of arcane magic that employs the blood of demons, the same rules would apply to it as arcane magic does, at the very least. However, fel magic users are most likely to be brought to execution without question in Night Elf territory. Metzen has said that demons and the like are not welcome in the city. He speaks about Stormwind and, ultimately, the Night Elves are a lot more strict about magic usage than the humans are.
Demon Hunters, as well, are outcasts and despised by the rest of Night Elf society. As well, Maiev killed a Demon Hunter by the name of Telarius Voidstrider in Darkshore. Since Illidan's escape took her from Hyjal to Azshara, this would mean this confrontation happened prior to her vendetta. This likely means she slew Telarius for being a Demon Hunter, as an official arm of Night Elf justice.
Night Elves seem to have a dislike for large-scale technology, like canons and other gnomish weapons of war. But this does not mean they are without technology. There is at least one case of clockwork, a simple music box. Night Elves are capable of operating firearms and have had access to gunpowder, via their fireworks, however, they still seem to prefer the bow.]
Wisps absorb stone, wood, and metal from the land and use these raw essences to grow buildings and other constructs as well as repairing them.