DTD Attribute Types - NMTOKENS
The attribute type of NMTOKENS allows the attribute value to be made up of multiple NMTOKENs, separated by a space.
Syntax:
<!ATTLIST element_name
attribute_name NMTOKENS default_value>
Example:
<!ATTLIST mountain
country NMTOKENS #REQUIRED>
Valid XML - The following XML document would be valid, as it conforms to the above DTD:
<mountains>
<mountain country="New Zealand">
<name>Mount Cook</name>
</mountain>
<mountain country="Australia">
<name>Cradle Mountain</name>
</mountain>
</mountains>
Invalid XML - The following XML document would be invalid because the value of the "country" attribute begins with a number (which means it's not a valid XML name):
<mountains>
<mountain country="1a">
<name>Mount Cook</name>
</mountain>
<mountain country="1b">
<name>Cradle Mountain</name>
</mountain>
</mountains>