Why in tld,you need add attribute type?

[Zhang Jones]

Firstly I want to say thank you for your help Stefan Evans ,you are a warm-hearted person! Thanks a lot!!!
Secondly, Why in tld,I need add attribute type?

<?xml version="1.0" encoding="UTF-8"?>
<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
		xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee/web-
		jsptaglibrary_2_0.xsd” version=”2.0">
 <tlib-version>1.0</tlib-version>
 <jsp-version>1.2</jsp-version>
 <uri>simpleTags</uri>
 
 <tag>
 	<description>worst use of a custom tag</description>
 	<name>SimpleTagTest</name>
 	<tag-class>edu.city.foo.SimpleTagTest</tag-class>
 	<!--<body-content>empty</body-content>-->
 	<body-content>scriptless</body-content>
 	
 	<attribute>
 		<name>movieList</name>
 		<required>true</required>
 		<rtexprvalue>true</rtexprvalue>
 		<type>java.util.List</type>
 	</attribute>
 </tag>
</taglib>

Lastly, how can I find thses <taglib xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee/web-
jsptaglibrary_2_0.xsd” version=”2.0">tag from docunent?