WoW API type: QuestString
Quest string and QuestLinks were added in patch 2.4.
Quest String FormattingEdit
Quest strings consist of the quest id and the quest level.
quest:questId:questLevel
Note that the quest id is actually used by wowhead and probably other sites - you can actually go to a quest page on wowhead, and change the end of the url to the in-game id, and you should get the page for that quest.