The domains attribute

The domains attribute lists the names of the domains in use by the current document type, and the ancestry for each domain. The domains attribute is declared on the root element for each topic type.

Each domain in use contributes a string in parentheses that gives the names of each ancestor domain plus the name of the contributing domain. Within each set of parentheses, the domain and its ancestry should be listed starting with the most distant ancestor (the root type off of which the domain hierarchy is based) and finishing with the name of the domain in use.

Example: task with three domains

<task id="mytask" class="- topic/topic task/task " 
	domains="(topic ui-d) (topic sw-d) (topic pr-d cpp-d)">
...
</task>
In this example, the task allows the use of tags for describing user interfaces (ui-d), software (sw-d), and also C++ programming (cpp-d).