public void setScratchId(int id) {
        scratchId = id;
    }
Returns whether this node is valid or not. When a child node from a SpanList, the child
is marked as invalid, and the reference to it is removed from the parent SpanList. However,
Annotations in the global list kept in SpanTree may still have references to the removed SpanNode.
Removing these references is costly, and is only done when calling {@link com.yahoo.document.annotation.SpanTree#cleanup()}.

@return true if this node is valid, false otherwise.
document/src/main/java/com/yahoo/document/annotation/SpanNode.java