-/** an element which matches exactly one input token */
-public abstract class Atom<T extends Token> extends Element {
+/**
+ * <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, that's sort of Frege'd
+ * up) so that Atoms can be intersected and unioned with each other
+ * to result in other Atom<Token>'s (rather than raw Topology<Token>'s, which
+ * are not Elements). If you want the latter, use the
+ * getTokenTopology() 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();
+
+ StringBuffer toString(StringBuffer sb) { sb.append(this); return sb; }