29.4 Document Type Definitions (cont.)

To specify finite choices:
<!ATTLIST price currency (USD | EUR | JPY) #REQUIRED>
Choices may contain letters, numbers, -, _ or .
currency attribute must be specified
Attribute Defaults:

Default Declaration	Explanation
`#REQUIRED`	Attribute is required
`#IMPLIED`	Attribute is optional
N	Default attribute, used if attribute not specified
`#FIXED` N	Attribute must either be unspecified or contain this value