BS ISO/IEC 29500-3:2015 pdf download-Information technology — Document description and processing languages — Office Open XML File Formats Part 3: Markup Compatibility and Extensibility.
6 Overview This clause is informative This Part of ISO/IEC 29500 describes a set of XML elements and attributes, called MCE elements and attributes, the purpose of which is to enable producing applications to guide consuming applications in their handling of any XML elements and attributes in namespaces not understood by the consuming applications. MCE elements and attributes are intended to enable producing applications to use features added in new versions or extensions of a markup specification in the production of new documents, which nevertheless remain interoperable with consuming applications that do not understand these features. A producing application includes MCE elements and attributes in documents to indicate to a consuming application how it can adjust the content of the document to exclude those features that are not compatible with the version of the markup specification that it understands, while at the same time allowing consuming applications that do understand these features to make full use of them. MCE elements and attributes define particular types of compatibility and extension constructs, as summarized below: · Namespaces can be declared to be ignorable, indicating that all elements and attributes in those namespaces can be disregarded by consuming applications as if they were not present in the input document, enabling graceful degradation of the document functionality. This allows implementations to identify some markup as not core to the document content. · Elements in ignorable namespaces can be marked for their content to be processed that would otherwise be ignored. This allows producing applications to prevent loss of content nested within an element in an ignorable namespace when processed by consuming applications that do not understand that namespace but do understand the namespace(s) of the nested content. · Namespaces can be declared that must be understood by consuming applications in order to process the document.