public DocumentSet preselect(DocumentSet in_docs) throws XPathException {
public DocumentSet preselect(DocumentSet in_docs, StaticContext context) throws XPathException {
	public DocumentSet preselect(DocumentSet in_docs) throws XPathException {		if (getLength() == 0)			return in_docs;		DocumentSet out_docs = getExpression(0).preselect(in_docs);		for (int i = 1; i < getLength(); i++)			out_docs = out_docs.intersection(getExpression(i).preselect(out_docs));		return out_docs;	}