In December 1998, our comrade Bert Bos released a W3C Note: List of suggested extensions to CSS. I thought it could be interesting to see where we stand 18 years later...

Id Suggestion
active WD CR, PR or REC Comment
1 Columns
2 Swash letters and other glyph substitutions
3 Running headers and footers
4 Cross-references
5 Vertical text
6 Ruby
7 Diagonal text through Transforms
7 Text along a path
8 Style properties for embedded 2D graphics ➡️ ➡️ through filters
9 Hyphenation control
10 Image filters
11 Rendering objects for forms
12 :target
13 Floating boxes to top & bottom of page
14 Footnotes
15 Tooltips possible with existing properties
16 Maths there was no proposal, only an open question
17 Folding lists possible with existing properties
18 Page-transition effects
19 Timed styles Transitions & Animations
20 Leaders
21 Smart tabs not sure it belongs to CSS
22 Spreadsheet functions does not belong to CSS
23 Non-rectangular wrap-around Exclusions, Shapes
24 Gradients Backgrounds & Borders
25 Textures/images instead of fg colors
26 Transparency opacity
27 Expressions partly calc()
28 Symbolic constants Variables
29 Mixed mode rendering
30 Grids for TTY
31 Co-dependencies between rules Conditional Rules
32 High-level constraints
33 Float: gutter-side/fore-edge-side
34 Icons & minimization
35 Namespaces
36 Braille
37 Numbered floats GCPM
38 Visual top/bottom margins
39 TOCs, tables of figures, etc.
40 Indexes
41 Pseudo-element for first n lines
42 :first-word
43 Corners border-radius and border-image
44 Local and external anchors Selectors level 4
45 Access to attribute values ➡️ access to arbitrary attributes hosted by arbitrary elements theough a selector inside attr() was considered and dropped
46 Linked flows Regions
47 User states
48 List numberings Counter Styles
49 Substractive text-decoration
50 Styles for map/area ➡️ ➡️ never discussed AFAIK
51 Transliteration ➡️ ➡️ discussed and dropped
52 Regexps in selectors
53 Last-of... selectors
54 Control over progressive rendering
55 Inline-blocks
56 Non-breaking inlines white-space applies to all elements since CSS 2.0...
57 Word-spacing: none
58 HSV or HSL colors
59 Standardize X colors
60 Copy-fitting/auto-sizing/auto-spacing Flexbox
61 @page inside @media
62 Color profiles dropped from Colors level 3 but in level 4
63 Underline styles
64 BECSS ➡️ ➡️ BECSS, dropped
65 // comments
66 Replaced elements w/o intrinsic size object-fit
67 Fitting replaced elements object-fit