[css2][css-2025] The state of modularization of CSS

[Crissov]

According to the 2025 Snapshot, the chapters, sections, subsections and sub-subsections of CSS Level 2.1 have been replaced / substituted / superceded and usually also extended by higher-level modules as follows (only highest-level heading shown):

• 1 About the CSS 2.1 Specification
  • 1.1 CSS 2.1 vs CSS 2
  • 1.2 Reading the specification
  • 1.3 How the specification is organized
  • 1.4 Conventions
    • 1.4.1 Document language elements and attributes
    • 1.4.2 CSS property definitions
      • 1.4.2.1 Value css-values-3
      • 1.4.2.2 Initial
      • 1.4.2.3 Applies to
      • 1.4.2.4 Inherited
      • 1.4.2.5 Percentage values
      • 1.4.2.6 Media groups
      • 1.4.2.7 Computed value
    • 1.4.3 Shorthand properties css-cascade-4 → css-cascade-5
    • 1.4.4 Notes and examples
    • 1.4.5 Images and long descriptions (css-images-3?)
  • 1.5 Acknowledgments
• 2 Introduction to CSS 2.1 recommended reading, unsubstituted
  • 2.1 A brief CSS 2.1 tutorial for HTML
  • 2.2 A brief CSS 2.1 tutorial for XML
  • 2.3 The CSS 2.1 processing model
    • 2.3.1 The canvas
    • 2.3.2 CSS 2.1 addressing model
  • 2.4 CSS design principles
• 3 Conformance: Requirements and Recommendations
  • 3.1 Definitions
  • 3.2 UA Conformance
  • 3.3 Error conditions
  • 3.4 The text/css content type
• 4 Syntax and basic data types (css-syntax-3, css-values-3)
  • 4.1 Syntax css-syntax-3
  • 4.2 Rules for handling parsing errors css-syntax-3
  • 4.3 Values css-values-3
  • 4.4 CSS style sheet representation css-syntax-3
• 5 Selectors selectors-3

• 6 Assigning property values, Cascading, and Inheritance (css-cascade-4, selectors-3)
  • 6.1 Specified, computed, and actual values css-cascade-4
  • 6.2 Inheritance css-cascade-4
  • 6.3 The @import rule css-cascade-4
  • 6.4 The cascade
    • 6.4.1 Cascading order css-cascade-4
    • 6.4.2 !important rules css-cascade-4
    • 6.4.3 Calculating a selector's specificity selectors-3 and css-cascade-4
    • 6.4.4 Precedence of non-CSS presentational hints css-cascade-4
• 7 Media types
  • 7.1 Introduction to media types
  • 7.2 Specifying media-dependent style sheets css-conditional-3
  • 7.3 Recognized media types mediaqueries-3 → mediaqueries-4
• 8 Box model
  • 8.1 Box dimensions css-box-3
  • 8.2 Example of margins, padding, and borders css-box-3
  • 8.3 Margin properties: 'margin-top', 'margin-right', 'margin-bottom', 'margin-left', and 'margin' css-box-3
    • 8.3.1 Collapsing margins explicitly not replaced yet
  • 8.4 Padding properties: 'padding-top', 'padding-right', 'padding-bottom', 'padding-left', and 'padding' css-box-3
  • 8.5 Border properties css-backgrounds-3
  • 8.6 The box model for inline elements in bidirectional context css-writing-modes-3 → css-writing-modes-4
• 9 Visual formatting model
  • 9.1 Introduction to the visual formatting model
    • 9.1.1 The viewport
    • 9.1.2 Containing blocks → css-display-3
  • 9.2 Controlling box generation
    • 9.2.1 Block-level elements and block boxes → css-display-3
      • 9.2.1.1 Anonymous block boxes explicitly not substituted yet
    • 9.2.2 Inline-level elements and inline boxes → css-display-3
      • 9.2.2.1 Anonymous inline boxes explicitly not substituted yet
    • 9.2.3 Run-in boxes → css-display-3
    • 9.2.4 The 'display' property → css-display-3
  • 9.3 Positioning schemes (→ css-position-3?)
    • 9.3.1 Choosing a positioning scheme: 'position' property
    • 9.3.2 Box offsets: 'top', 'right', 'bottom', 'left'
  • 9.4 Normal flow
    • 9.4.1 Block formatting contexts
    • 9.4.2 Inline formatting contexts
    • 9.4.3 Relative positioning
  • 9.5 Floats (extended by → css-shapes-1)
    • 9.5.1 Positioning the float: the 'float' property
    • 9.5.2 Controlling flow next to floats: the 'clear' property
  • 9.6 Absolute positioning (→ css-position-3?)
    • 9.6.1 Fixed positioning
  • 9.7 Relationships between 'display', 'position', and 'float' 🔜 css-display-3
  • 9.8 Comparison of normal flow, floats, and absolute positioning
    • 9.8.1 Normal flow
    • 9.8.2 Relative positioning
    • 9.8.3 Floating a box
    • 9.8.4 Absolute positioning
  • 9.9 Layered presentation
    • 9.9.1 Specifying the stack level: the 'z-index' property
  • 9.10 Text direction: the 'direction' and 'unicode-bidi' properties css-writing-modes-3 → css-writing-modes-4
• 10 Visual formatting model details → css-sizing-3 (overlaying)

• 11 Visual effects
  • 11.1 Overflow and clipping
    • 11.1.1 Overflow: the 'overflow' property
    • 11.1.2 Clipping: the 'clip' property → css-masking-1
  • 11.2 Visibility: the 'visibility' property
• 12 Generated content, automatic numbering, and lists
  • 12.1 The :before and :after pseudo-elements
  • 12.2 The 'content' property
  • 12.3 Quotation marks
    • 12.3.1 Specifying quotes with the 'quotes' property
    • 12.3.2 Inserting quotes with the 'content' property
  • 12.4 Automatic counters and numbering
    • 12.4.1 Nested counters and scope
    • 12.4.2 Counter styles (css-counter-styles-3)
    • 12.4.3 Counters in elements with 'display: none'
  • 12.5 Lists
    • 12.5.1 Lists: the 'list-style-type', 'list-style-image', 'list-style-position', and 'list-style' properties
• 13 Paged media
  • 13.1 Introduction to paged media
  • 13.2 Page boxes: the @page rule
    • 13.2.1 Page margins
    • 13.2.2 Page selectors: selecting left, right, and first pages
    • 13.2.3 Content outside the page box
  • 13.3 Page breaks → css-break-3
  • 13.4 Cascading in the page context
• 14 Colors and Backgrounds (css-backgrounds-3, css-color-4 → css-color-5)
  • 14.1 Foreground color: the 'color' property css-color-4 → css-color-5
  • 14.2 The background css-backgrounds-3
• 15 Fonts css-fonts-3 → css-fonts-4

• 16 Text → css-text-3 (→ css-text-decor-3)
  • 16.1 Indentation: the 'text-indent' property → css-text-3
  • 16.2 Alignment: the 'text-align' property → css-text-3
  • 16.3 Decoration → css-text-decor-3
  • 16.4 Letter and word spacing: the 'letter-spacing' and 'word-spacing' properties → css-text-3
  • 16.5 Capitalization: the 'text-transform' property → css-text-3
  • 16.6 White space: the 'white-space' property → css-text-3
• 17 Tables
  • 17.1 Introduction to tables
  • 17.2 The CSS table model
    • 17.2.1 Anonymous table objects
  • 17.3 Columns
  • 17.4 Tables in the visual formatting model
    • 17.4.1 Caption position and alignment
  • 17.5 Visual layout of table contents
    • 17.5.1 Table layers and transparency
    • 17.5.2 Table width algorithms: the 'table-layout' property
      • 17.5.2.1 Fixed table layout
      • 17.5.2.2 Automatic table layout
    • 17.5.3 Table height algorithms
    • 17.5.4 Horizontal alignment in a column
    • 17.5.5 Dynamic row and column effects
  • 17.6 Borders
    • 17.6.1 The separated borders model
      • 17.6.1.1 Borders and Backgrounds around empty cells: the 'empty-cells' property
    • 17.6.2 The collapsing border model
      • 17.6.2.1 Border conflict resolution
    • 17.6.3 Border styles
• 18 User interface
  • 18.1 Cursors: the 'cursor' property css-ui-3
  • 18.2 System Colors css-color-4 → css-color-5
  • 18.3 User preferences for fonts
  • 18.4 Dynamic outlines: the 'outline' property css-ui-3
  • 18.5 Magnification
• Appendix A → css-speech-1
  • Appendix A.2.1–3 css-values-3
• Appendix G css-syntax-3

Specifications with a rightwards arrow in front are not quite interoperable, references in parentheses or with a question mark are only implied as substitutes by the Snapshot.

Sections §4, §5, §6, §14, §15, §16 have basically been replaced by mature modules already, sections §7, §8 and §10 are almost there (going only by the latest Snapshot). The others have only partially been superceded yet. I believe §9, §11 and §18 are better covered by stable specifications than documented. This could and should be improved.

Is there some umbrella specification that should replaces the remainder of sections §1, §2 and §3?

This would leave §12 (generated content, css-gcpm-3, with pseudo elements and lists), §13 ([css-page-3]) and §17 (css-tables-3) as the major missing modules.

Related: #4752