The Layer > Select command allows you to select a single markup layer and perform an operation, such as changing the color, unloading, deleting, and so forth. For example, if you have several layers displayed (each containing several elements), click Layer > Select and click to select an element. Each element in that layer is selected. You can then change the elements on that layer.
This command is available only when one or more markup layers are displayed in the Detail File Viewer window.