Learning XML, 2nd Edition

The Area Model

In XSL all the positioning, shaping, and spacing of elements on the page takes place inside of areas. An area is an abstract framework used to represent a piece of the formatted document. It contains all the geometric and stylistic information needed to position and render its children correctly. Areas are nested, leading to the concept of an area tree. From the root node, all the way down to the areas containing glyphs and images, a formatted document is completely described by an area tree.

A formatting object tree produces an area tree the way an architectural model leads to a final set of blueprints. Strictly speaking, there is not a one-to-one mapping between formatting objects and areas. An FO can create zero or more areas, and each area is usually produced by a single FO. There are exceptions, however, as in the case of ligatures, which are single glyphs created through the contribution of two or more character objects.

Associated with an area is a collection of details that completely describe its geometry and rendering. These traits, as they are called, are derived either directly from formatting object properties or indirectly as a result of calculations involving other traits. These traits are the final, precise data that drive the rendering process in the formatter.

Areas are divided into two types: block and inline. Blocks and inlines have been described thoroughly in previous chapters and they behave essentially the same here. An area may have block ...