Specify whether an acitivty's task state should always be maintained by the system, or if it is allowed to reset the task to its initial state in certain situations.

Normally the system will reset a task (remove all activities from the stack and reset the root activity) in certain situations when the user re-selects that task from the home screen. Typically this will be done if the user hasn't visited that task for a certain amount of time, such as 30 minutes.

By setting this attribute, the user will always return to your task in its last state, regardless of how they get there. This is useful, for example, in an application like the web browser where there is a lot of state (such as multiple open tabs) that the application would not like to lose.

Must be a boolean value, either "true" or "false".

This may also be a reference to a resource (in the form "@[package:]type:name") or theme attribute (in the form "?[package:][type:]name") containing a value of this type.

[Android Documentation]