protected boolean matchesStartAnchor(RuleEvaluation e) {
        if (anchor != Anchor.START && anchor != Anchor.BOTH) return true;
        if (e.getPosition() == 0) return true;
        if (e.getTraceLevel() >= 4)
            e.trace(4, this + " must be at the start, which " + e.currentItem() + " isn't");
        return false;
    }
Check start anchor. Trace level 4 if no match
container-search/src/main/java/com/yahoo/prelude/semantics/rule/Condition.java