Below is a snippet from the XMLSchema

<xs:complexType name="nameType">
               <xs:sequence>
                       <xs:element minOccurs="0" ref="desig"/>
               </xs:sequence>
               <xs:attribute ref="dest" use="required"/>
               <xs:attribute ref="id"/>
               <xs:attribute ref="garageid"/>
               <xs:attributeGroup ref="xlink:XLINKATT1"/>
       </xs:complexType>
<xs:attribute name="id" type="xs:ID"/>

this means that in the XML, the nameType node can be identified by the
id attribute as xs:attribute name=id is mapped to XS:ID.

Likewise there can be many nodes in the XML that has ID associated to it.

<xml>
<root>
<somenode>
<nameType id="2" attrib2="34">text</nameType>
<nameType id="3" attrib2="34">text</nameType>
<nameType id="4" attrib2="34">text</nameType>
</somenode>
<anothernode attrib5="55"/>
</root>