public void checkArguments(ExpressionVisitor visitor) throws XPathException {
if (checked) return;
checked = true;
super.checkArguments(visitor);
if (argument[1] instanceof StringLiteral) {
StaticContext env = visitor.getStaticContext();
if (env instanceof ExpressionContext) {
// We're in XSLT
String formatString = ((StringLiteral)argument[1]).getStringValue();
StructuredQName formatQName = null;