code: private final void assertIsLocPathIterator(Expression expr1, ExpressionOwner eo) 
      throws RuntimeException 
    {
  		if(!(expr1 instanceof LocPathIterator))
  		{
  			String errMsg;
  			if(expr1 instanceof Variable)
  			{
  				errMsg = "Programmer's assertion: expr1 not an iterator: "+
  				          ((Variable)expr1).getQName();
  			}
  			else
  			{
  				errMsg = "Programmer's assertion: expr1 not an iterator: "+
  				          expr1.getClass().getName();
  			}
  			throw new RuntimeException(errMsg + ", "+
  				          eo.getClass().getName()+" "+
  				          expr1.exprGetParent());
  		}
    }
docs: Assert that the expression is a LocPathIterator, and, if
  not, try to give some diagnostic info.