Appendix B: Changes from CSS1
Appendix B. Changes from CSS1
This appendix is informative, not normative.
CSS2 builds on CSS1 and all valid CSS1 style sheets are valid CSS2 style sheets. The changes between the CSS1 specification (see [CSS1]) and this specification fall into three groups: new functionality, updated descriptions of CSS1 functionality, and changes to CSS1.
In addition to the functionality of CSS1, CSS2 supports:
- The concept of media types.
- The 'inherit' value for all properties.
- Paged media
- Aural style sheets
- Several internationalization features, including list numbering styles, support for bidirectional text, and support for language-sensitive quotation marks.
- An extended font selection mechanism, including intelligent matching, synthesis, and downloadable fonts. Also, the concept of system fonts has been is introduced, and a new property, 'font-size-adjust', has been added.
- Tables, including new values on 'display' and 'vertical-align'.
- Relative and absolute positioning, including fixed positioning.
- New box types (along with block and inline): compact and run-in.
- The ability to control content overflow, clipping, and visibility in the visual formatting model.
- The ability to specify minimum and maximum widths and heights in the visual formatting model.
- An extended selector mechanism, including child selectors, adjacent selectors, and attribute selectors.
- Generated content, counters and automatic numbering, and markers.
- Text shadows, through the new 'text-shadow' property.
- Several new pseudo-classes, :first-child, :hover, :focus, :lang.
- System colors and fonts.
- Dynamic outlines.
The CSS1 specification was short and concise. This specification is much more voluminous and more readable. Much of the additional content describes new functionality, but the description of CSS1 features has also been extended. Except in a few cases described below, the rewritten descriptions do not indicate a change in syntax nor semantics.
While all CSS1 style sheets are valid CSS2 style sheets, there are a few cases where the CSS1 style sheet will have a different meaning when interpreted as a CSS2 style sheet. Most changes are due to implementation experience feeding back into the specification, but there are also some error corrections.
- The meaning of "!important" has been changed. In CSS1, "!important" in an author's style sheet took precedence over one in a user style sheet. This has been reversed in CSS2.
- In CSS2 color values are clipped with regard to the device gamut, not with regard to the sRGB gamut as in CSS1.
- CSS1 simply said that 'margin-right' was ignored if the both 'margin-left' and 'width' were set. In CSS2 the choice between relaxing 'margin-right' or 'margin-left' depends on the writing direction.
- In CSS1, several properties (e.g., 'padding') had values referring to the width of the parent element. This was an error; the value should always refer to the width of a block-level element and this specification reflects this by introducing the term "containing block".
- The initial value of 'display' is 'inline' in CSS2, not 'block' as in CSS1.
- In CSS1, the 'clear' property applied to all elements. This was an error, and the property only applies to block-level elements in CSS2.
- In CSS1, ':link', ':visited' and ':active' were mutually exclusive; in CSS2, ':active' can occur together with ':link' or ':visited'.
- The suggested scaling factor between adjacent 'font-size' indexes in the table of font sizes has been reduced from 1.5 to 1.2.
- The computed value, not the actual value, of 'font-size' is inherited.
- The CSS1 description of 'inside' (for 'list-style-position') allowed the interpretation that the left margin of the text was affected, rather than the position of the bullet. In CSS2 that interpretation is ruled out.
- Please also consult the normative section on the differences between the CSS1 and CSS2 tokenizer.