From MTG Salvation Wiki
Detain is a keyword action that was introduced in Return to Ravnica. Dragon's Maze added 2 cards with detain. In effect, for one round of turns, it is an Arrest or Faith's Fetters for any permanent.
- Activated abilities include a colon and are written in the form “[cost]: [effect].” No one can activate any activated abilities, including mana abilities, of a detained permanent.
- The static abilities of a detained permanent still apply. The triggered abilities of a detained permanent can still trigger.
- If a creature is already attacking or blocking when it’s detained, it won’t be removed from combat. It will continue to attack or block.
- If a permanent’s activated ability is on the stack when that permanent is detained, the ability will be unaffected.
- If a noncreature permanent is detained and later turns into a creature, it won’t be able to attack or block.
- When a player leaves a multiplayer game, any continuous effects with durations that last until that player's next turn or until a specific point in that turn will last until that turn would have begun. They neither expire immediately nor last indefinitely.
- Dave Guskin. (November 02, 2012.) "Article I: Fun (see also Subsections F, J, and V.14.k)", Daily MTG, magicthegathering.com, Wizards of the Coast.