Deciding the proper format organization
Where possible, keep the organization of formats very simple and straightforward. When properly designed, formats should work as layers of refinement. Lower-level formats create various components, and higher-level formats assemble them.
When deciding how to partition a layout into formats, the rules of thumb are:
The basic concept of a format is similar to that of a subroutine. And the process of how to break down a layout problem into discreet layout components is similar to how one would break down a task into subroutines.
More specifically, formats are manipulating objects, and thus many of the guidelines of good object-oriented design apply to creating formats.
Component-level formats compose single layout elements. Examples are Navigation tools, titles, headers footnotes, and so on. These should be designed as completely stand-alone items, so that they can be used in as wide a variety of contexts as possible.
Mid-level formats compose structural elements from lower-level elements. Examples are formats for header sections, body sections, footnote sections, tables, lists, and so on. These formats cannot work properly unless they can manipulate the lower-level components generically. So that puts the onus on designers of low-level components to fully encapsulate the elements they create.
Page-layout formats compose entire pages, and well-designed page formats mainly assemble mid-level structures and components and apply styles. As a rule, page-layout formats should be very generic, and invoke other formats to construct the components that they position and style. They should allow for many sub-elements to be optional
Really well-designed page formats can produce a wide variety of looks, because they can adjust layouts based upon the presence of absence of lower elements.
Site-layout formats define the overall structure and look of a website. They can control which page-layout formats are applied to which pages, how the site navigation will work, and determine the location and usage of resources.
In a well-designed site, the page-layout formats invoke the site-layout formats to locate resources, such as images, styles and scripts, and to define policy. This allows the page-layout scripts to again be designed as context-free as possible.