The structure of a page communicates much of how we understand a text (Mountford 1990). Material at the top written in larger type, often centred, is usually a title. A number in the upper or lower (occasionally the outer) margin is a page number (note how odd it would be to have the page number in the middle of the inside margin). A small raised number in the text is a footnote reference. At the beginning of a book, a list of terms followed by numbers is likely a table of contents; at the end of a book, a list of terms followed by numbers is likely an index. The table of contents and the index are sometimes labeled as such, but even without the labels, we recognize them by their position in the book. Correspondence has a fairly fixed format: date, salutation, text, closing signature. Letters in French used to start halfway down the page. [emphasis mine] In German letters, the salutation ends in an exclamation mark; in English, a comma or colon is used, with a sociolinguistic difference of formality.
Henry Rogers, Writing Systems (2004), pages 15-16.