public static final Reagent ELEMENT = new SimpleReagent("ELEMENT", "descendant-or-self::text()", ReagentType.PHRASE,
Element.class, "Element representing either a principal or a target.");
public Formula getFormula() {
Reagent[] reagents = new Reagent[] {ELEMENT};
return new SimpleFormula(GroupKeyOrLiteralPhrase.class, reagents);
}