The Sheet model is a very simple model which allows the user to format and to paginate sequences of paragraphs without specifying a more complex structure. Nevertheless, complex elements such as tables or drawing can be included in a Sheet.
A Sheet is composed of a sequence of Paragrs which can be of type Paragraph, Picture, Graphics or Other_type (i.e. any other object defined by a structure schema).
Two presentation schemas are proposed for the Sheet model: ``portrait'' and ``landscape''.