Requirements for specialized element types and attributes

When you specialize one element from another, or a new attribute from @props or @base, the new element or attribute must obey certain rules in order to be a conforming specialization.

A specialized element:

An attribute specialized from the @props or @base attribute:

DITA elements are never in a namespace. Only the @DITAArchVersion attribute is in a DITA-defined namespace. All other attributes, except for those defined by the XML standard, are in no namespace.

This limitation is imposed by the details of the @class attribute syntax, which makes it impractical to have namespace-qualified names for either vocabulary modules or individual element types or attributes. Elements included as descendants of the DITA <foreign> element type may be in any namespace.
Note: For this reason, domain modules that are intended for wide use should take care to define element type and attribute names that are unlikely to conflict with names used in other domains, for example, by using a domain-specific prefix on all names.

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OASIS DITA Version 1.2 -- OASIS Standard, 1 December 2010
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