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7.3. CSS Modularization (CSS3)

In the draft stages of CSS modularization, the effort appears to focus on not only a division of CSS attributes into logical groups, but also on a division of labor. With modularization, pieces of the standard, such as specifications for selectors, value types, and content models (box and line models, for example), can be developed individually. Implementation reasons still apply to the impetus behind the move toward modularization. A browser intended for visual display of content, for instance, shouldn't be expected to include style sheet attributes for aural styles.

Table 7-2 presents a preliminary list of modules that may comprise CSS3. Several categories in this list are new to CSS, rather than simply reorganized CSS2 features. Even if not every module is complete when other CSS3 modules are firmed up, others can be added as they are ready.

Table 7-2. Preliminary CSS3 modules




Selector types and specificity

Values and units

Value types (e.g., lengths, colors) and their representation

Value assignment, cascade, and inheritance

How styles impact elements (e.g., specified versus computed values), cascading rules, attribute inheritance chains

Box model/vertical

Block layout: borders, margins, padding, overflow, clipping, and visibility


Positioning, floating layout

Color/gamma/color profiles

Foreground color, gamma correction

Colors and Backgrounds

Background images and colors

Line box model

Inline element rendering

Text/bidi/vertical alignment

Text decoration, line height, spacing, transforms, and alignment


Font-related attributes


CSS-based ruby text attributes

Generated content/markers

List styles, automatic counters, :before and :after pseudo-elements

Replaced content

Replaced content attributes

Paged media

Page breaks, running headers and footers, cross-reference pointers

User interface

Form element styles, cursors, kiosk mode display


Web-enhanced font attributes


Aural styles and accessibility enhancements


CSS connection to Synchronized Multimedia standards


Table-related attributes


Multi-column layout


CSS connection to Scalable Vector Graphics standard


Rendering math expressions (Math Markup Language standard)


Scripted behaviors extension

Media queries

Applying styles based on quantitative features supported by media (e.g., screen size)


Basic syntax, including namespaces

Test suite

Specific examples and guidelines

Several CSS3 modules listed in Table 7-2 either represent entirely new CSS features or include expanded features of existing CSS2 areas. The list is also ambitious in that a few modules point to W3C work that is far from finished.

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