while (sit.hasNext()) {
AttributeSet next = sit.next().getAttributeSet();
Iterator<Attribute<Object>> ait = attrMap.keySet().iterator();
while (ait.hasNext()) {
Attribute<Object> attr = ait.next();
if (next.containsAttribute(attr)) {
Object v = attrMap.get(attr);
if (v != null && !v.equals(next.getValue(attr))) {
attrMap.put(attr, null);
}
} else {