What type of materials should contain content of interest to motivated readers but does not fit in the main publication?

Supplemental materials are designed to support the main publication by providing additional information or data that may be of interest to readers who want to delve deeper into a subject. These materials serve as complementary content, offering insights that enhance understanding without disturbing the flow or structure of the primary publication. Such materials often include detailed methodologies, extensive datasets, or additional figures that could be overwhelming if included in the main text.

In contrast, the main text focuses on presenting core findings and essential information in a concise manner. Appendices also serve a similar purpose as supplemental materials by including extra content that is pertinent but not critical to the primary discussion. However, the option specifically stated as supplemental materials highlights their intended role in catering to motivated readers looking for more in-depth exploration of the topic. Business correspondence, while it may contain relevant details, is typically unrelated to the content of formal publications and thus does not fit within the scope of this question.