Introduction to Parameter Entities

This section describes each parameter entity in the NCBI Collection and NCBI Book Tag Sets as well as those in the base Suite that are used by these Tag Sets, except those that are part of the MathML or the XHTML Table structure. (Note: The math and table modules come from external sources and not maintained with these Tag Sets or base Suite; see the documentation provided by the authority responsible for the MathML Tag Set or XHTML table model.)

A parameter entity is an XML syntactic construct that allows a name to be given to a collection of elements, attributes, or attribute values so that they can be referred to by name rather than have their members listed every time they are used. For example, the name %person-name.class; stands for all the element components of a person’s name, such as any title or honorific preceding the person’s name, a given (first) name, a surname, and any suffix following the name (such as “Jr.”).

Parameter Entity Pages

Although the parameter entities are declared in many different modules, they are described here in alphabetical order of their XML names (i.e., parameter entity type names). The XML name is the shorter machine-readable name used in DTD fragments and schemas and by software; for example, the XML name %app.class; is used for the parameter entity named Just Appendix Class Elements. Parameter entity names always begin with a percent sign and end with a semi-colon.

Each parameter entity is described by a separate HTML page, where the heading for the page displays the parameter entity’s XML name followed by a more descriptive name. The rest of the parameter entity description page discusses aspects of the parameter entity and its usage. These sections within the page always appear in the following order, although any given parameter entity description may not contain all the sections:


This section provides a narrative description of the parameter entity, describing what it contains, what it does, or why and when it should be used.


This section provides additional useful information about the parameter entity or its usage.

Design Notes are instructions aimed at implementors, so they may better appreciate the rationale underlying a design decision such as the inclusion of an OR bar within a parameter entity. For example, inline-mix parameter entities always begin with an OR bar to ease customization for those organizations wishing only character data rather than a mixed content model for a particular element.

Content Model

Contains a copy of the parameter entity’s declaration in XML syntax, i.e., the “content” of the parameter entity. This may contain embedded parameters entities, of the form “%name;”.

Expanded Content Model

Contains a copy of the parameter entity’s declaration in XML syntax, i.e., the “content” of the parameter entity with all embedded parameter entities expanded to their ultimate values.


This portion names the base Suite module in which the parameter entity is defined. In those instances in which the Suite’s declaration for a parameter entity has been overridden by a Tag-Set-specific override module, the name of the Tag-Set-specific override module will be named instead.

Parameter Entity Naming Conventions

These Tag Sets and Suite modules have used a series of design and naming conventions consistently. While parsing software cannot enforce these parameter entity usage or naming conventions, these conventions can make it much easier for a person to know how the content models work. The NCBI Book Tag Set and NCBI Collection Tag Set (as well as the entire Archiving and Interchange Suite) use the following usage and naming conventions.