A textdisplay object refers to a "canvas" that can contain many items of text (textitems).
Each display can be seen by multiple observers (players) and each observer can see multiple displays. For example, you could have a display that showed a score, and a display that showed information specific to one team, such as the location of a flag. Every player would be an observer of the first display and each team would have their own display that its players would be observers of.
Related scripting functions