In Project Navigator 9.2i and earlier, there were four selectable "User Constraints" options available when a UCF file was selected in the Sources window (Create Timing Constraints, Assign Package Pins, Create Area Constraints, and Edit Constraints (Text)).
In Project Navigator 10.1, the only option available is Edit Constraints (Text).
As part of the changes related to allowing multiple User Constraint File (UCF) support in ISE 10.1, the process tree for a UCF was updated to include only the "Edit Constraints (Text)" process.
The Constraints Editor and Floorplan Editor are still available by double-clicking the UCF by selecting the appropriate preference. Select Edit -> Preferences -> ISE General -> Editors. Under Constraints Entry, select Constraints Editor, Floor Plan Editor, or Text Editor to select the desired constraint entry method obtained by double-clicking the UCF.
In ISE 11.1, PlanAhead will replace Constraints Editor and Floorplan Editor for FPGA timing and location constraints processes.