Classification domain elements

In this section:

1. subjectref
   The <subjectref> element identifies a subject to classify content. The <subjectref> can identify the subject with a keyref attribute (if the scheme has a <subjectdef> with a keys attribute that assigns a key to the subject) or an href attribute (if the scheme is not available and a topic exists that defines the subject).
2. topicapply
   The <topicapply> element identifies subjects that qualify the content for filtering or flagging but not retrieval. The <topicapply> element can identify a single subject. Additional subjects can be specified by nested <subjectref> elements.
3. topicsubject
   The <topicsubject> element identifies the subjects covered by a topic or map.
4. topicSubjectTable
   The <topicSubjectTable> element is a specialized relationship table which allows a map to use relationship tables to associate topics with subjects. Tools (such as search tools) may use these classifications to retrieve content that is relative to a specific subject or combination of subjects.
5. topicSubjectHeader
   The <topicSubjectHeader> element specifies constraints on the subjects used in classifications.
6. topicSubjectRow
   The <topicSubjectRow> is a grouping element that contains one row of a subject table. It contains topic references in the first column, and relates those references to the subjects in each following column.
7. topicCell
   The <topicCell> element contains topics that will be associated with subjects in each following column of the current row in the <topicSubjectTable>.
8. subjectCell
   The <subjectCell> element contains subjects that are associated with topics in the first column of the current row in the <topicSubjectTable>. The subjects themselves have no defined relationship across columns, other than the fact that they apply to the same content.