A document contains one or more sections.

A section contains one or more column layouts. A section optionally may contain a header and a footer.

A column layout contains columns. It also contains the text that is laid out in the columns.

A column is a rectangle in which text is displayed. Text flows between the columns in a column layout.

Headers and footers repeat on successive pages of the section. Text does not flow between them, so they do not use columns.