Once a program has been read into a ctedit, it is possible to select parts of the tree, for editing purposes, or other environmental needs as we will see later on. A select is the ctedit's way of displaying a Centaur variable's selection information. A select is only visible (and thus the selection it refers to) when the correct select resource indicates its background and foreground colors and priority.
The current selection is used by Centaur to designate a current subtree or subtrees. It is used for pointing and editing. In the environment section of this tutorial, we will add other selections to the Centaur variable when it contains an Exp tree.