Admonitions are cautions, warnings, or other types of notifications to the reader that emphasize the importance of specific information.

Base elements mark a specific spot in a document which can be cross-referenced to output a page or chapter number.

Compound elements have layers of nested elements that are required to preserve a specific complex structure.

Descriptions provide some information about the document.

Divisions are major sections of a document like preface, chapter, appendix. They have headings to demarcate the document, and they might have page breaks associated with them.

Document information is front matter such as author and product name.

When an element has a formal and an informal form, the formal has a title and the informal does not.

General elements include such elements as emphasis, citation, and many others that do not fit specific categories.

Index provides the elements used for marking content to be used in the index.

When an element has a formal and an informal form, the formal has a title and the informal does not.

Inline are elements that do not cause a new line to start before or after them. They remain in the line of text where they are inserted.

Line specific are overrides of the FOSI that allow you to duplicate file contents, screen contents, or other content where you want line breaks and space to match what is being depicted exactly.

Links are used for creating hyperlinks.

Lists are vertically positioned elements used for various lists such as numbered lists and bulleted lists.

Paragraphs are the variations of paragraphs defined in your DTD, such as the formal and simple paragraphs.

Reference are footnotes and cross references.

Synopsis contain some subset of allowed elements that have meaning when assembled but not individually (for example, commands and functions).

Technical are specific to computers. There are elements for hardware names, operating systems, errors, interfaces, and more.

All the elements in the DTD (if Smart Insert is checked), or all available at the insertion point (if Smart Insert is not checked).