Specialized processing is not necessary for every specialized element, only for those elements which do not have appropriate default behavior based on their ancestors.
Whether creating a new transform or extending an existing one, there are several rules that should be followed to ensure the effectiveness of the transform for other specialized types, and also the maintainability and extensibility of the transform to accommodate new requirements.
OASIS DITA Architectural Specification v1.0 -- 09 May 2005
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