Value of an attribute is the same as the value we prescribe in the schema, whether or not the attribute is present : Attribute « XML Schema « XML Tutorial

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2. XML Schema
3. Attribute

File: Schema.xsd
<?xml version = "1.0" ?>
<schema xmlns= "http://www.w3.org/2001/XMLSchema">
<element name = "CreditAccount">
   <complexType>
      <sequence>
         <element name = "AccountName" type = "string" />
         <element name = "AccountNumber" type = "integer" />
         <element name = "Amount" type = "string" />
      </sequence>
      <attribute name = "currency" fixed = "US$" />
   </complexType>
</element>
</schema>

File: Data.xml
<?xml version = "1.0" ?>
<CreditAccount currency = "AUS$">
   <AccountName>Joe</AccountName>
   <AccountNumber>2701 2202</AccountNumber>
   <Amount>200.00</Amount>
</CreditAccount>