Spoiler Alert: Discussion of the phasing technology used in Cataclysm, it’s history, application and the problems surrounding it. Some allusion to in-game events/quests, although no specific details.
Back in Vanilla, Warcraft was mainly a scattering of quest hubs, each with their localised set of quests. Sure there may have been prerequisites such as a minimum level, but by and large you could quest where you liked. In Cataclysm the experience is streamlined into quest tunnels that guide you through a zone from one end to the other. To help with this, phasing is the toy of choice in the quest designer’s toolbox.
Phasing as a technology started out with a single quest in Burning Crusade. “Intercepting the Mana Cells” was added in patch 2.4.0 as part of the daily quests for the Shattered Sun Offensive. These quests were part of the overall Sunwell Plateau content update, adding the final dungeons and raid instances before the release of Wrath. In the quest, the player used a device to move “out of phase” and be able to interact with the items they needed to complete the quest.