A table of contents, usually heaed simply "Contents," is a list of the parts of a book or document (including Acts of Parliaments) organized in the order in which the parts appear. The contents usually includes the titles or descriptions of the first-level headers, such as chapter titles in longer works, and often includes second-level or section titles (A-heads) within the chapters as well, and occasionally even third-level titles (subsections or B-heads). The depth of detail in tables of contents depends on the length of the work, with longer works having less. Formal reports (ten or more pages and being too long to put into a memo or letter) also have tables of contents. Documents of fewer than ten pages do not require tables of contents, but often have a short list of contents at the beginning.