-/** <font color=green>an element which matches exactly one input token</font> */
-public abstract class Atom<T> extends Element implements Topology<Atom<T>> {
+/**
+ * <font color=green>
+ * an element which matches some set of one-token-long input strings
+ * </font>.
+ *
+ * <p>
+ * This class is a topology over itself (yes, this is impredicative).
+ * This means that you can call Atom.union(Atom) and get back an Atom.
+ * If you are interested in the topology of <i>tokens</i> which this
+ * Atom can match, use the <tt>getTokenTopology()</tt> method.
+ * </p>
+ */
+public abstract class Atom<Token>
+ extends Element
+ implements Topology<Atom<Token>> {
+
+ /** the set (topology) of tokens that can match this element */
+ public abstract Topology<Token> getTokenTopology();