Other Modifications: Classifying a Role

The Role attribute, found on almost all of the elements in DocBook, is a CDATA attribute that can be used to subclass an element. In some applications, it may be useful to modify the definition of Role so that authors must choose one of a specific set of possible values.

In Example 5-14, Role on the Procedure element is constrained to the values Required or Optional.

Example 5-14. Changing Role on Procedure

<!ENTITY % procedure.role.attrib "Role (Required|Optional) #IMPLIED">
<!-- load DocBook -->
<!ENTITY % DocBookDTD PUBLIC "-//OASIS//DTD DocBook V3.1//EN">
%DocBookDTD;