public void sortChildrenRecursive() {
        for (SpanNode node : children()) {
            if (node instanceof SpanList) {
                ((SpanList) node).sortChildrenRecursive();
            }
            Collections.sort(children());
        }
    }
Recursively sorts all children by occurrence in the text covered.
document/src/main/java/com/yahoo/document/annotation/SpanList.java