Introduction to Elements

This section describes elements specific to the NCBI Historical DTD; elements previously declared in the NCBI Book DTD or base Suite have not been included, with the exception of the <annotation> and <named-content> elements, which have acquired new usages and thus need new descriptions. All other elements are defined and provided with examples in the Tag Library for the NCBI Book DTD. Although the elements are declared in several modules, they are described here in alphabetical order of their tag names (i.e., element type names). The tag name is the shorter machine-readable name used in tagged documents, in the DTDs/schemas, and by XML software; for example, the tag name <alt-term> is used for the element named Alternative Version of a Term.

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


Provides a narrative description of the element, that is, it “defines” the element and may provide information on its usage. This is not intended to be a formal dictionary definition, but more to provide information about an element and how it may be used.


This section (when present) provides additional information about the element, explanations of similar or contrasting elements, or instructions for element usage. (See also Related Elements described below.)

Conversion Notes are explicit and sometimes very technical instructions to people who are mapping between the NCBI Historical DTD and other DTDs, or who are building conversion software to convert between another DTD and a DTD written from this Suite. They may be more technical than a general reader will need to worry about.

Authoring Notes are usage instructions aimed at persons writing or editing books according to an authoring DTD written from this Suite.

Implementor’s Notes are instructions written to persons creating or maintaining DTDs based on the Suite, for example, information explaining that the Chemical Markup Language has not been included in the base Suite and where and how it could be included.


For an element that may take attributes, this section contains an alphabetical list of those attributes. Each line contains the identification for one attribute: first, the attribute’s name as it appears in the DTD, then a longer, more descriptive name. Full attribute definitions are not provided; instead, each attribute is linked to its description in the Attribute Section, which follows the Element Description Section in this Tag Library.

Related Elements

Contains information about elements associated with the current element. For example, the <page-start> element serves as a wrapper element for two elements, <page-num> and <running-head>. In order to better understand the relationship of these components, information about all of them may be provided in the Related Elements section for each element. Similarly, the relationship between a Historical DTD element such as <alt-term> and base Suite elements such as <annotation> may be discussed. (Note: While theoretically, information on related elements is provided here, and information about contrasting elements is provided in the Remarks section, in practice the two sections may overlap, with elements associated with the current element discussed in Remarks or with contrasting elements explained in Related Elements.)

Model Information

Content Model

Contains a copy of the element’s declaration from the DTD, i.e., the “content” of an element as shown in XML syntax. For those users not versed in XML syntax, a description in plain English follows.


Contains a description of the “content” of the element, that is, what is allowed to be inside the element, for example, whether it may contain text, other elements, or both text and others elements in some combination. This content description contains the same information in plain English phrasing that the DTD provides in XML syntax. For example, the description of an element may contain, “text, numbers, and special characters”, which means it contains ordinary text. If an element contains other elements, their names are listed here.

Context Table Section

The Tag Library contains a complete context table providing information about where any element can be used. This section contains the portion of the context table relevant to the element being discussed, that is, a listing of the elements which may contain the element under discussion.

Tagged Example

This portion of the element description page provides an excerpt of a tagged XML document, showing use of the current element. Usually an element is shown in context, with its surrounding elements, and the current element is highlighted in bold.

Module (Implementor Information)

Names the module from the NCBI Historical DTD, NCBI Book DTD, or NCBI Suite in which the element is defined. If an element is defined only in the base Suite, the base module name is given. In those instances in which a Book DTD module (prefixed “bookcustom-”) over-rides the Suite’s declaration for an element, the name of the DTD-specific over-ride module is given instead. Similarly, if an element declaration from one of the Historical modules (prefixed “historical-”) over-rides a Book customization, the name of the Historical module is given.