For the purposes of this specification, the following definitions apply. Other terms are defined where they appear in italics type. Terms explicitly defined in this specification are not to be presumed to refer implicitly to similar terms defined elsewhere. [e: This part uses OPC-related terms, which are defined in Part 2: "Open Packaging Conventions". ]

Throughout this specification, the terms namespace declaration, namespace name, qualified name, expanded name, prefixed name, unprefixed name, and local name shall have the meanings as defined in the W3C Recommendation, “Namespaces in XML 1.0 (Second Edition).”

alternate content — A set of markup alternatives, of which no more than one shall be processed by a markup consumer. A markup consumer chooses from among the alternatives based upon its set of understood namespaces.

compatibility-rule attribute — An XML attribute described in this specification that expresses rules governing markup consumers’ behavior when encountering XML elements and attributes from non-understood namespaces.

ignore — To disregard the presence of an element or attribute, processing the markup as if that element or attribute did not exist.

markup consumer — A tool that can read and parse a markup document and further conforms to the requirements of a markup specification.

markup document — An XML document that conforms to the requirements of a markup specification.

markup editor — A tool that acts as a markup consumer in reading a markup document, makes changes to that markup, and acts as the producer of the modified markup.

markup preprocessor — A software module, designed for use in the implementation of markup consumers, that follows the rules of this Markup Compatibility and Extensibility specification to remove or replace all elements and attributes from the Markup Compatibility namespace, all elements and attributes from ignorable non-understood namespaces, and all elements and attributes from subsumed namespaces..

markup producer — A tool that can generate a markup document, and conforms to a markup specification.

markup specification — An XML-based markup format specification that incorporates all of the requirement of this Part.

namespace, ignorable — A namespace, identified in markup, whose elements and attributes shall be ignored by a markup consumer that does not understand that namespace.

namespace, understood — An XML namespace containing any recognized XML elements or attributes.

preserve —To retain an ignored element or attribute during the course of editing.

recognize — To have knowledge of the correct interpretation of an XML element, XML attribute, or attribute-value, as defined in a markup specification.