public void backtrack() {
        state.backtrack(owner);
        if (owner.getTraceLevel()>=5)
            owner.trace(5,"Backtracked to " + owner.currentItem() + " for '" + condition + "'");
    }
Backtrack to the evaluation state at the point where this choicepoint were instantiated.
container-search/src/main/java/com/yahoo/prelude/semantics/engine/Choicepoint.java