# Derivatives and Integrals: An Annotated Discourse

## Section33Ancillaries

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Once your content is in place, you can begin thinking about various useful derivative works. A natural example for a textbook is an “Instructor’s Version”. Various switches for hints, answers, and solutions to exercises would allow you to include more of these for the use of just an instructor. Here we also demonstrate the <commentary> element. It is similar in many ways to a <paragraphs> in that it can be placed within any division and must be titled. The main difference is that it is not displayed by default, so you must set the string parameter commentary to the value yes. Other distinctions are:
• Since it is elective, you need to be careful about cross-references to and from a <commentary>. It is highly likely that you will want to make cross-references within a <commentary> pointing to other portions of your text, and this is always a good idea. You will want to avoid making cross-references to a <commentary> from other parts of the text, with the exception of a cross-reference that originates within some <commentary>.
• Numbered items are prohibited within a <commentary>, such as a <figure> or a <theorem>. Doing so would disrupt consecutive numbering in different versions, with or without, <commentary> included. Numbered equations are not prohibited in the schema, but should definitely be avoided anyway.
After some nonsense text in a paragraph, there is a <commentary> with two paragraphs. For the online version of this sample article, we have enabled commentaries. But if you are experimenting yourself, you will want to be aware if you are enabling these or not.
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