Specialization elements

Several DITA elements exist either for architectural reasons or for support of specialized markup yet to be designed. Although there is little need to use these elements unless you are directed to, some of them, such as <boolean> and <state>, can be used if your content makes use of these semantic distinctions. A discussion of signals on a gate of an integrated logic circuit, for example, might use the state element to represent either on or off conditions of that gate.

boolean
The <boolean> element is used to express one of two opposite values, such as yes or no, on or off, true or false, high or low, and so forth. The element itself is empty; the value of the element is stored in its state attribute, and the semantic associated with the value is typically in a specialized name derived from this element. If you need more than two values (for example, "yes," "no" and "don't care") use the <state> element instead. This element is primarily for specialization, where it can be used to require a logical true or false designation in a particular part of the document.
itemgroup
The <itemgroup> element is reserved for use in specializations of DITA. As a container element, it can be used to sub-divide or organize elements that occur inside a list item, definition, or parameter definition.
no-topic-nesting
The <no-topic-nesting> element is a placeholder in the DITA architecture. It is not actually used by the default DITA document types; it is for use only when creating a validly customized document type where the information designer wants to eliminate the ability to nest topics. Not intended for use by authors, and has no associated output processing.
required-cleanup
A <required-cleanup> element is used as a placeholder for migrated elements that cannot be appropriately tagged without manual intervention. As the element name implies, the intent for authors is to clean up the contained material and eventually get rid of the <required-cleanup> element. Authors should not insert this element into documents.
state
The <state> element specifies a name/value pair whenever it is necessary to represent a named state that has a variable value. The element is primarily intended for use in specializations to represent specific states (like logic circuit states, chemical reaction states, airplane instrumentation states, and so forth).
term
The <term> element identifies words that may have or require extended definitions or explanations. In future development of DITA, for example, terms might provide associative linking to matching glossary entries.