World of Warcraft was first announced by Blizzard at the ECTS trade show in September 2001. Development of the game took about five years with extensive testing done to make sure everything was ready for launch. The 3-D graphics in WoW use elements of the proprietary graphics engine originally used in Warcraft III. The game was designed to be an open environment where players are allowed to do what they please, alongside optional quests that players can complete to advance further in the game. In addition, the quests were made to help guide players to spread across different zones to try to avoid what developers called 'player collision'. The game interface was also designed to be easy to use allowing players to customize areas to their likings and also allows for add-ons and other modifications.