public void setStartIndex(int startIndex) {
        if (startIndex < 0) {
            throw new IllegalArgumentException("A start index less than 0 is not valid.");
        }
        this.startIndex = startIndex;
    }
Sets the index of the first result to return. For example, if the start index is set to 20, the Iterator returned
will start at the 20th result in the query. This method can be used in combination with
{@link #setNumResults(int)} to perform pagination of results.

@param startIndex the index of the first result to return.
xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/PubsubNodeResultFilter.java