When a player dies, they will "watch" ("spectate") their killer the moment they die for a brief period of time before respawning. This is similar to most FPS games.
Players in death spectating mode will not be able to move or do anything other than spectate at their death location (duh), chat, and use a set of commands that you allow (such as /me, /msg, etc.)
Unlike some other plugins, this one attempts to maintain compatiblity with existing plugins, particularly those that handle death and respawning (PlayerDeathEvent and PlayerRespawnEvent). There are some minor caveats due to manually performing this sort of compatibility, primarily because the player does not "actually" die or respawn. But the difference in experience is far better when a player does not "actually" die. More info here on that (and a small story of how this plugin came to be) if you're interested: //TODO: add sway.com presentation here