Learning XML, 2nd Edition

Formatting Objects

Formatting objects (FOs) are the building blocks of the transformation result tree that drives the formatter. They are compact containers of content and style with all the information necessary to generate a presentable formatted document.

There are two major kinds of FO. Flow objects create areas and appear inside flows. (A flow is a continuous stream of text that may be broken across pages.) Layout objects, or auxiliary objects, help produce areas by contributing parameters.

A block object creates a region of content to be inserted into a flow, so it qualifies as a flow object. In contrast, the initial-page-number FO resets the count of page numbering. Since it only contributes some information to aid in processing, rather than create regions on its own, it is a layout object.

An FO document structure is a tree, like any other XML document. Every element in it is a formatting object, so we call it an FO tree. The root of this tree is a root element. Its children include:

layout-master-set

This element contains page layout descriptions.

declarations

Optional, this element contains global settings that will affect overall formatting.

page-sequence

One or more of these elements contain flow objects that hold the content of the document.

In the coming sections, I will break down this structure further, starting with page layout. From there, we will move to flows, blocks, and finally inlines.

Page Layout

Contained in the layout-master-set object are specifications ...