Can we have space in a bean's id value in spring

Question

I am getting this error:

org.xml.sax.SAXParseException: cvc-datatype-valid.1.2.1: 'duke duke' is not a valid value for 'NCName'.

I am using this spring-config.xml:

<?xml version="1.0" encoding="UTF-8"?>
beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
bean id="duke duke"
    class="Juggler"/>
/beans>

My bean id's value has spaces in between.

This is my main class:

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;


public class Main {

    public static void main(String[] args)
    {
        ApplicationContext ctx=new ClassPathXmlApplicationContext("config/spring-config.xml");
        Juggler jg=(Juggler)ctx.getBean("duke duke");
        jg.perform();        
    }
}

However if I change the xsd in spring-config to spring-beans-3.1.xsd. I don't get this error. Why is it so??