XML Schema for multiple email recipients - regex

Question

I need a sample XSD to support multiple email recipients in a new element. I require each recipient email address in a different element. Can anyone help me with explanation?
Example:
<EmailReceipts>
<address1></address1>
<address2></address2>
</EmailReceipts>

Answer 1

First off, I'd recommend not embedding an index number in the address elements:
<EmailReceipts>
<address>john#example.com</address>
<address>mary#example.org</address>
</EmailReceipts>
Then this XSD will validate the above XML (as well as other XML documents with additional address elements):
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="EmailReceipts">
<xs:complexType>
<xs:sequence>
<xs:element name="address" maxOccurs="unbounded" type="xs:string"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
The above XSD will allow any string contents for the address elements. If you've like to be more strict, you could use a regular expression to limit the values for address:
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="EmailReceipts">
<xs:complexType>
<xs:sequence>
<xs:element name="address" maxOccurs="unbounded" type="EmailAddressType"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:simpleType name="EmailAddressType">
<xs:restriction base="xs:string">
<xs:pattern value="([0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*#([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9})"/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
Note that the above regular expression is one of many possible, each having various degrees of generality and specificity over a syntax that is more involved than you might imagine.