Structured Books and TOCs (attributes)

Typically, the book itself can be a structured document which contains the book root element that contains the elements corresponding to the root elements in each of the documents in the book. The unstructured content (TEXT) can be wrapped in a special TOC element. The TOC element becomes simply another element within the book's root element. Then the TOC element can have attributes itself, as your other MainChapter elements do.

Instead of the above, you can put attributes in the book's root element that are then seen by all the chapters, as well as the TOC element, in the book. This allows you to set them in only one place, rather than in each chapter.

If your book file does not have structure, you can likely wrap the unstructured content of the TOC with a MainChapter element (IF the MainChapter element allows TEXT alone) and set the attributes in the MainChapter element. Each time you update the book you MAY have to rewrap the TOC's unstructured content. I worked at a company years ago that used this approach; updating the book did not always replace the previous unstructured content with the updated content. I found the workaround was to delete the previous content from the TOC element before updating the book.

In my CURRENT work, my EDD has a TableOfContents element that can contain only TEXT. The unstructured TOC file is in the book but placed at the end of the book file. THEN I open the table of contents FILE (the one containing the TableOfContents ELEMENT) and import the unstructured TOC file into the TableOfContents element BY REFERENCE (the unstructured TOC file becomes a text inset inside the TableOfContents element). This avoids having to delete the content of the TableOfContents element before updating the book; however, you have to update the book twice, once to update the unstructured TOC content and once to update the text inset of the TableOfContents element. It may sound complicated, but it works.