An enhancement set is a group of enhancements that grants set bonuses when multiple enhancements from the set are slotted in the same power.
Most set enhancements work like other enhancements, boosting one or more aspects of a power. The strength of these boosts depends on the set enhancement's level, not its level relative to the character. In particular, set enhancements are never outleveled by a character, and there is no maximum level to slot them. The minimum level to slot them is three levels below the enhancement's level, except very rare and superior archetype enhancements. Very rare set enhancements and superior archetype enhancements have enhancement values 1/4th higher than standard, but only exist as level 50 enhancements and can only be slotted by level 50 characters.
Some set enhancements add effects known as procs to their slotted powers. Some set enhancements grant bonuses directly, whether combined with other enhancements in the set or not.
Two identical set enhancements cannot be slotted into the same power in the same build, but can be slotted into different powers, unless unique. If unique, only one of that enhancement may be slotted per build. Different levels of the same enhancement still count as identical for this purpose. Archetype enhancements and superior archetype enhancements of the same type also count as identical for this purpose.
Up to five of the same bonus can be granted to a character at a time. Different values of the same type of bonus count as different for this purpose. Set bonuses and bonuses granted directly by special enhancements also count as different for this purpose.