From 4497a71e9a5453fd18894f016779769eb16b0db3 Mon Sep 17 00:00:00 2001 From: Florian Rivoal Date: Mon, 31 Jan 2022 14:08:35 +0900 Subject: [PATCH] [css-2022] Set up 2022 snapshot Includes 'hyphenate-character' as a shippable property, as per #6887 --- css-2022/Overview.bs | 1064 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 1064 insertions(+) create mode 100644 css-2022/Overview.bs diff --git a/css-2022/Overview.bs b/css-2022/Overview.bs new file mode 100644 index 00000000000..21afd2e4ed8 --- /dev/null +++ b/css-2022/Overview.bs @@ -0,0 +1,1064 @@ +
+Title: CSS Snapshot 2022
+Shortname: css-2022
+Level: none
+Status: ED
+Group: CSSWG
+Work Status: revising
+URL: https://drafts.csswg.org/css-2022/
+Editor: Tab Atkins Jr., Google, http://xanthir.com/, w3cid 42199
+Editor: Elika J. Etemad / fantasai, Invited Expert, http://fantasai.inkedblade.net/contact, w3cid 35400
+Editor: Florian Rivoal, Invited Expert, https://florian.rivoal.net, w3cid 43241
+Abstract: This document collects together into one definition all the specs that
+	together form the current state of Cascading Style Sheets (CSS) as of 2022.
+	The primary audience is CSS implementers, not CSS authors, as this definition
+	includes modules by specification stability, not Web browser adoption rate.
+Status Text:
+	This document is a work in progress,
+	aimed at representing the state of CSS as of 2022.
+	It should become a Working Group Note when completed.
+
+	
+Boilerplate: index no
+
+
+spec:selectors-4; type:selector; text::lang()
+
+
+ + + + + +Introduction {#intro} +===================== + + When the first CSS specification was published, + all of CSS was contained in one document that defined CSS Level 1. + CSS Level 2 was defined also by a single, multi-chapter document. + However for CSS beyond Level 2, + the CSS Working Group chose to adopt a modular approach, + where each module defines a part of CSS, + rather than to define a single monolithic specification. + This breaks the specification into more manageable chunks + and allows more immediate, incremental improvement to CSS. + + Since different CSS modules are at different levels of stability, + the CSS Working Group has chosen to publish this profile + to define the current scope and state of Cascading Style Sheets as of 2022. + +

+Background: The W3C Process and CSS

+ + This section is non-normative. + + In the W3C Process, + a Recommendation-track document passes through three levels of stability, + summarized below: + +
+
Working Draft (WD) +
+ + This is the design phase of a W3C spec. + The WG iterates the spec in response to internal and external feedback. + + The first official Working Draft is designated the “First Public Working Draft” (FPWD). + In the CSSWG, publishing FPWD indicates that the Working Group as a whole has agreed to work on the module, + roughly as scoped out and proposed in the editor's draft. + + The transition to the next stage is sometimes called “Last Call Working Draft” (LCWD) phase. + The CSSWG transitions Working Drafts once we have resolved all known issues, + and can make no further progress without feedback from building tests and implementations. + + This “Last Call for Comments” sets a deadline for reporting any outstanding issues, + and requires the WG to specially track and address incoming feedback. + The comment-tracking document is the Disposition of Comments (DoC). + It is submitted along with an updated draft for the Director's approval, + to demonstrate wide review and acceptance. + +
Candidate Recommendation (CR) +
+ This is the testing phase of a W3C spec. + Notably, this phase is about using tests and implementations to test the specification: + it is not about testing the implementations. + This process often reveals more problems with the spec, + and so a Candidate Recommendation will morph over time in response to implementation and testing feedback, + though usually less so than during the design phase (WD). + + Demonstration of two correct, independent implementations of each feature is required to exit CR, + so in this phase the WG builds a test suite and generates implementation reports. + + The transition to the next stage is “Proposed Recommendation” (PR). + During this phase the W3C Advisory Committee must approve the transition to REC. + +
Recommendation (REC) +
+ This is the completed state of a W3C spec and represents a maintenance phase. + At this point the WG only maintains an errata document + and occasionally publishes an updated edition that incorporates the errata back into the spec. +
+ + An Editor's Draft is effectively a live copy of the editors’ own working copy. + It may or may not reflect Working Group consensus, + and can at times be in a self-inconsistent state. + (Because the publishing process at W3C is time-consuming and onerous, + the Editor's Draft is usually the best (most up-to-date) reference for a spec. + Efforts are currently underway to reduce the friction of publishing, + so that official drafts will be regularly up-to-date + and Editor's Drafts can return to their original function as scratch space.) + + +

+Classification of CSS Specifications

+ + Advisement: + A list of all CSS modules, stable and in-progress, + and their statuses + can be found at the CSS Current Work page. + + +

Cascading Style Sheets (CSS) — The Official Definition

+ + This profile includes only specifications that we consider stable + and for which we have enough implementation experience that we are sure of that stability. + + Note: This is not intended to be a CSS Desktop Browser Profile: + inclusion in this profile is based on feature stability only + and not on expected use or Web browser adoption. + This profile defines CSS in its most complete form. + + As of 2022, + Cascading Style Sheets (CSS) is defined by the following + specifications. + +
+
CSS Level 2, latest revision (including errata) + [[!CSS2]] +
+ This defines the core of CSS, parts of which are overridden by later specifications. + We recommend in particular reading Chapter 2, + which introduces some of the basic concepts of CSS + and its design principles. + +
CSS Syntax Level 3 + [[!CSS-SYNTAX-3]] +
+ Replaces CSS2§4.1, CSS2§4.2, CSS2§4.4, and CSS2§G, + redefining how CSS is parsed. + +
CSS Style Attributes + [[!CSS-STYLE-ATTR]] +
+ Defines how CSS declarations can be embedded in markup attributes. + +
Media Queries Level 3 + [[!CSS3-MEDIAQUERIES]] +
+ Replaces CSS2§7.3 and expands on the syntax for media-specific styles. + +
CSS Conditional Rules Level 3 + [[!CSS-CONDITIONAL-3]] +
+ Extends and supersedes CSS2§7.2, + updating the definition of ''@media'' rules to allow nesting + and introducing the ''@supports'' rule for feature-support queries. + +
Selectors Level 3 + [[!SELECTORS-3]] +
+ Replaces CSS2§5 and CSS2§6.4.3, defining an extended range of selectors. + +
CSS Namespaces + [[!CSS3-NAMESPACE]] +
+ Introduces an ''@namespace'' rule to allow namespace-prefixed selectors. + +
CSS Cascading and Inheritance Level 4 + [[!CSS-CASCADE-4]] +
+ Extends and supersedes CSS2§1.4.3 and CSS2§6, as well as [[CSS-CASCADE-3]]. + Describes how to collate style rules and assign values to all properties on all elements. + By way of cascading and inheritance, values are propagated for all properties on all elements. + +
CSS Values and Units Level 3 + [[!CSS-VALUES-3]] +
+ Extends and supersedes CSS2§1.4.2.1, CSS2§4.3, and CSS2§A.2.1–3, + defining CSS's property definition syntax + and expanding its set of units. + +
CSS Custom Properties for Cascading Variables Module Level 1 + [[!CSS-VARIABLES-1]] +
+ Introduces cascading variables as a new primitive value type that is accepted by all CSS properties, + and custom properties for defining them. + +
CSS Box Model Level 3 + [[!CSS-BOX-3]] +
+ Replaces CSS2§8.1, §8.2, §8.3 (but not §8.3.1), and §8.4. + +
CSS Color Level 3 + [[!CSS-COLOR-3]] +
+ Extends and supersedes CSS2§4.3.6, CSS2§14.1, and CSS2§18.2, + introducing an extended range of color values. + Also introduces the 'opacity' property. + +
CSS Backgrounds and Borders Level 3 + [[!CSS-BACKGROUNDS-3]] +
+ Extends and supersedes CSS2§8.5 and CSS2§14.2, + providing more control of backgrounds and borders, + including layered background images, + image borders, + and drop shadows. + +
CSS Images Level 3 + [[!CSS-IMAGES-3]] +
+ Redefines and incorporates the external 2D image value type, + introduces native 2D gradients, + and adds additional controls for replaced element sizing and rendering. + +
CSS Fonts Level 3 + [[!CSS-FONTS-3]] +
+ Extends and supersedes CSS2§15 + and provides more control over font choice and feature selection. + +
CSS Writing Modes Level 3 + [[!CSS-WRITING-MODES-3]] +
+ Defines CSS support for various international writing modes, + such as left-to-right (e.g. Latin or Indic), + right-to-left (e.g. Hebrew or Arabic), + bidirectional (e.g. mixed Latin and Arabic) and vertical (e.g. Asian scripts). + Replaces and extends CSS2§8.6 and §9.10. + +
CSS Multi-column Layout Level 1 + [[!CSS-MULTICOL-1]] +
+ Introduces multi-column flows to CSS layout. + +
CSS Flexible Box Module Level 1 + [[!CSS-FLEXBOX-1]] +
+ Introduces a flexible linear layout model for CSS. + +
CSS User Interface Module Level 3 + [[!CSS-UI-3]] +
+ Extends and supersedes CSS2§18.1 and CSS2§18.4, + defining 'cursor', 'outline', and several new CSS features that also enhance the user interface. + +
CSS Containment Module Level 1 + [[!CSS-CONTAIN-1]] +
+ Introduces the 'contain' property, + which enforces the independent CSS processing of an element’s subtree + in order to enable heavy optimizations by user agents when used well. + +
CSS Transforms Level 1 + [[!CSS-TRANSFORMS-1]] +
+ Introduces coordinate-based graphical transformations to CSS. + +
CSS Compositing and Blending Level 1 + [[!COMPOSITING]] +
+ Defines the compositing and blending of overlaid content + and introduces features to control their modes. + +
CSS Easing Functions Level 1 + [[!CSS-EASING-1]]. +
+ Describes a way for authors to define a transformation + that controls the rate of change of some value. + Applied to animations, + such transformations can be used to produce animations + that mimic physical phenomena such as momentum + or to cause the animation to move in discrete steps producing robot-like movement. + +
CSS Counter Styles Level 3 + [[!CSS-COUNTER-STYLES-3]] +
+ Introduces the ''@counter-style'' rule, + which allows authors to define their own custom counter styles + for use with CSS list-marker and generated-content counters [[CSS-LISTS-3]]. + It also predefines a set of common counter styles, + including the ones present in CSS2 and CSS2.1. +
+ + Note: Although we don't anticipate significant changes to the specifications that form this snapshot, + their inclusion does not mean they are frozen. + The Working Group will continue to address problems as they are found in these specs. + Implementers should monitor www-style + and/or the CSS Working Group Blog + for any resulting changes, corrections, or clarifications. + +

+Fairly Stable Modules with limited implementation experience

+ + The following modules have completed design work, + and are fairly stable, + but have not received much testing and implementation experience yet. + We hope to incorporate them into the [[#css|official definition of CSS]] in a future snapshot. + +
+
Media Queries Level 4 + [[MEDIAQUERIES-4]] +
+ Extends and supersedes [[CSS3-MEDIAQUERIES]], + expanding the syntax, deprecating most media types, + and introducing new media features. + +
CSS Color Level 4 + [[!CSS-COLOR-4]] +
+ Extends and supersedes [[CSS-COLOR-3]], + further expanding the range of colors expressible in CSS. + +
CSS Display Module Level 3 + [[CSS-DISPLAY-3]] +
+ Replaces CSS2§9.1.2, §9.2.1 (but not §9.2.1.1), §9.2.2 (but not §9.2.2.1), §9.2.3, and §9.2.4 (and lays the foundations for replacing §9.7), + defining how the CSS formatting box tree is generated + from the document element tree + and defining the 'display' property that controls it. + +
CSS Writing Modes Level 4 + [[CSS-WRITING-MODES-4]] +
+ Extends and supersedes [[CSS-WRITING-MODES-3]], + adding more options for vertical writing. + +
CSS Fragmentation Module Level 3 + [[CSS-BREAK-3]] +
+ Describes the fragmentation model that partitions a flow into pages, columns, or regions + and defines properties that control it. + Extends and supersedes CSS2§13.3. + +
CSS Box Alignment Module Level 3 + [[CSS-ALIGN-3]] +
+ Introduces properties to control the alignment of boxes + within their containers in the various CSS box layout models: + block layout, table layout, flex layout, and grid layout. + +
CSS Shapes Module Level 1 + [[CSS-SHAPES-1]] +
+ Extends floats (CSS2§9.5) to effect non-rectangular wrapping shapes. + +
CSS Text Module Level 3 + [[CSS-TEXT-3]] +
+ Extends and supersedes CSS2§16 excepting §16.2, + defining properties for text manipulation and specifying their processing model. + It covers line breaking, justification and alignment, white space handling, and text transformation. + +
CSS Text Decoration Level 3 + [[CSS-TEXT-DECOR-3]] +
+ Extends and supersedes CSS2§16.3, + providing more control over text decoration lines + and adding the ability to specify text emphasis marks + and text shadows. + +
CSS Masking Level 1 + [[CSS-MASKING-1]] +
+ Replaces CSS2§11.1.2 + and introduces more powerful ways of clipping and masking content. + +
CSS Scroll Snap Module Level 1 + [[CSS-SCROLL-SNAP-1]] +
+ Contains features to control panning and scrolling behavior with “snap positions”. + +
CSS Speech Module Level 1 + [[CSS-SPEECH-1]] +
+ Replaces CSS2§A, + overhauling the (non-normative) speech rendering chapter. + +
CSS Scrollbars Styling Module Level 1 + [[CSS-SCROLLBARS-1]] +
+ Defines properties to influence the visual styling of scrollbars, + introducing controls for their color and width. +
+ +

+Modules with Rough Interoperability

+ + Although the following modules have been widely deployed with rough interoperability, + their details are not fully worked out or sufficiently well-specified + and they need more testing and bugfixing. + We hope to incorporate them into the [[#css|official definition of CSS]] in a future snapshot. + +
+
CSS Transitions Level 1 + [[CSS-TRANSITIONS-1]] + and CSS Animations Level 1 + [[CSS-ANIMATIONS-1]]. +
+ Introduces mechanisms for transitioning the computed values of CSS properties over time. + +
CSS Grid Layout Module Level 1 + [[!CSS-GRID-1]] +
+ Introduces a two-dimensional grid-based layout system, + optimized for user interface design. + In the grid layout model, the children of a grid container + can be positioned into arbitrary slots in a predefined flexible or fixed-size layout grid. + +
CSS Grid Layout Module Level 2 + [[!CSS-GRID-2]] +
+ Extends and supersedes [[CSS-GRID-1]], + introducing “subgrids” for managing nested markup in a shared grid framework. + +
CSS Will Change Level 1 + [[CSS-WILL-CHANGE-1]] +
+ Introduces a performance hint property called 'will-change'. + +
Filter Effects Module Level 1 + [[FILTER-EFFECTS-1]] +
+ Introduces filter effects as a way of processing an element’s rendering before it is displayed in the document. + +
CSS Font Loading Module Level 3 + [[CSS-FONT-LOADING-3]] +
+ Introduces events and interfaces used for dynamically loading font resources. + +
CSS Box Sizing Level 3 + [[!CSS-SIZING-3]] +
+ Overlays and extends CSS§10., + expanding the value set of the sizing properties, + introducing more precise sizing terminology, + and defining with more precision and detail + various automatic sizing concepts only vaguely defined in CSS2. + + +
CSS Transforms Level 2 + [[!CSS-TRANSFORMS-2]] +
+ Builds upon [[CSS-TRANSFORMS-1]] + to add new transform functions and properties for three-dimensional transforms, + and convenience functions for simple transforms. + +
CSS Lists and Counters Module Level 3 + [[!CSS-LISTS-3]] +
+ Contains CSS features related to list counters: + styling them, + positioning them, + and manipulating their value. + +
CSS Logical Properties and Values Level 1 + [[!CSS-LOGICAL-1]] +
+ Introduces logical properties and values + that provide the author with the ability to control layout through logical, + rather than physical, + direction and dimension mappings. + Also defines logical properties and values for the features defined in [[CSS2]]. + These properties are writing-mode relative equivalents + of their corresponding physical properties. + +
CSS Positioned Layout Module Level 3 + [[!CSS-POSITION-3]] +
+ Contains defines coordinate-based positioning and offsetting schemes of CSS: + [=relative positioning=], + [=sticky positioning=], + [=absolute positioning=], + and [=fixed positioning=]. + +
Resize Observer + [[!RESIZE-OBSERVER-1]] +
+ This specification describes an API for observing changes to element’s principal box's size. + +
Web Animations + [[!WEB-ANIMATIONS-1]] +
+ Defines a model for synchronization and timing of changes to the presentation of a Web page. + Also defines an application programming interface for interacting with this model. + +
CSS Fonts Module Level 4 + [[!CSS-FONTS-4]] +
+ Extends and supersedes CSS Fonts 3 + and provides more control over font choice and feature selection, + including support for OpenType variations. + +
CSS Color Adjustment Module Level 1 + [[!CSS-COLOR-ADJUST-1]] +
+ This module introduces a model and controls over automatic color adjustment by the user agent to handle user preferences and device output optimizations. +
+ +

+CSS Levels

+ + Cascading Style Sheets does not have versions in the traditional sense; + instead it has levels. Each level of CSS builds on the previous, + refining definitions and adding features. The feature set of each higher + level is a superset of any lower level, and the behavior allowed for a given + feature in a higher level is a subset of that allowed in the lower levels. + A user agent conforming to a higher level of CSS is thus also conformant to + all lower levels. + +
+
CSS Level 1 +
+ The CSS Working Group considers the + CSS1 specification to be + obsolete. CSS Level 1 is defined as all the features defined + in the CSS1 specification (properties, values, at-rules, etc), but using + the syntax and definitions in the + CSS2.1 specification. + CSS Style Attributes + defines its inclusion in element-specific style attributes. + +
CSS Level 2 +
+ Although the CSS2 specification + is technically a W3C Recommendation, it passed into the Recommendation stage + before the W3C had defined the Candidate Recommendation stage. Over time + implementation experience and further review has brought to light many problems + in the CSS2 specification, so instead of expanding an already unwieldy + errata list, the CSS Working Group chose to define CSS Level 2 + Revision 1 (CSS2.1). In case of any conflict between the two specs + CSS2.1 contains the definitive definition. + + Once CSS2.1 became Candidate Recommendation—effectively though not + officially the same level of stability as CSS2—obsoleted the CSS2 + Recommendation. Features in CSS2 that were dropped from CSS2.1 should be + considered to be at the Candidate Recommendation stage, but note that many + of these have been or will be pulled into a CSS Level 3 working draft, in + which case that specification will, once it reaches CR, obsolete the + definitions in CSS2. + + The CSS2.1 specification defines + CSS Level 2 and the CSS + Style Attributes specification defines its inclusion in + element-specific style attributes. + +
CSS Level 3 +
+ CSS Level 3 builds on CSS Level 2 module by module, using the CSS2.1 + specification as its core. Each module adds functionality and/or + replaces part of the CSS2.1 specification. The CSS Working Group + intends that the new CSS modules will not contradict the CSS2.1 + specification: only that they will add functionality and refine + definitions. As each module is completed, it will be plugged in to + the existing system of CSS2.1 plus previously-completed modules. + + From this level on modules are levelled independently: for example + Selectors Level 4 may well be completed before CSS Line Module Level 3. + Modules with no CSS Level 2 equivalent start at Level 1; + modules that update features that existed in CSS Level 2 start at Level 3. + +
CSS Level 4 and beyond +
+ There is no CSS Level 4. + Independent modules can reach level 4 or beyond, + but CSS the language no longer has levels. + ("CSS Level 3" as a term is used only to differentiate it from the previous monolithic versions.) +
+ +

+CSS Profiles

+ + Not all implementations will implement all functionality defined in CSS. + + In the past, the Working Group published a few Profiles, + which were meant to define the minimal subset of CSS + that various classes of user agents were expected to support. + + This effort has been discontinued, + as the Working Group was not finding it effective or useful, + and the profiles previously defined are now unmaintained. + + Note: Partial implementations of CSS, even if that subset is an official profile, + must follow the forward-compatible parsing rules for partial implementations. + +

+Requirements for Responsible Implementation of CSS

+ + The following sections define several conformance requirements + for implementing CSS responsibly, + in a way that promotes interoperability in the present and future. + +

Partial Implementations

+ + So that authors can exploit the forward-compatible parsing rules to assign fallback values, + CSS renderers must treat as invalid + (and ignore as appropriate) + any at-rules, properties, property values, keywords, and other syntactic constructs + for which they have no usable level of support. + In particular, user agents must not selectively ignore + unsupported property values and honor supported values in a single multi-value property declaration: + if any value is considered invalid (as unsupported values must be), + CSS requires that the entire declaration be ignored. + +

Implementations of Unstable and Proprietary Features

+ + To avoid clashes with future stable CSS features, + the CSSWG recommends the following best practices for the implementation of + unstable features and proprietary extensions to CSS: + +

+Experimentation and Unstable Features

+ + Implementations of unstable features + that are described in W3C specifications + but are not interoperable + should not be released broadly for general use; + but may be released for limited, experimental use in controlled environments. + +
+ Why? + We want to allow both authors and implementors to experiment with the feature and give feedback, + but prevent authors from relying on them in production websites + and thereby accidentally "locking in" (through content dependence) + certain syntax or behavior that might change later. +
+ +
+ For example, + a UA could release an unstable features for experimentation + through beta or other testing-stage builds; + behind a hidden configuration flag; + behind a switch enabled only for specific testing partners; + or through some other means of limiting dependent use. +
+ + A CSS feature is considered unstable until + its specification has reached the Candidate Recommendation (CR) stage in the W3C process. + In exceptional cases, + the CSSWG may additionally, by an officially-recorded resolution, + add pre-CR features to the set that are considered safe to release for broad use. + See [[#CR-exceptions]]. + + Note: Vendors should consult the WG explicitly and not make assumptions on this point, + as a pre-CR spec that hasn't changed in awhile is usually more out-of-date than stable. + +

+Proprietary and Non-standardized Features

+ + To avoid clashes with future CSS features, + the CSS2.1 specification reserves a + prefixed syntax [[!CSS2]] + for proprietary and experimental extensions to CSS. + A CSS feature is a proprietary extension if it is meant for use + in a closed environment accessible only to a single vendor's user agent(s). + A UA should support such proprietary extensions + only through a vendor-prefixed syntax + and not expose them to open (multi-UA) environments such as the World Wide Web. + +
+ Why? + The prefixing requirement allows shipping specialized features in closed environments + without conflicting with future additions to standard CSS. + The restriction on exposure to open systems is to prevent + accidentally causing the public CSS environment + to depend on an unstandardized proprietary extensions. +
+ +
+ For example, + Firefox's XUL-based UI, Apple's iTunes UI, and Microsoft's Universal Windows Platform app + use extensions to CSS implemented by their respective UAs. + So long as these UAs do not allow Web content to access these features, + they do not provide an opportunity for such content + to become dependent on their proprietary extensions. +
+ + Even if a feature is intended to eventually be used in the Web, + if it hasn't yet been standardized + it should still not be exposed to the Web. + + +

+Market Pressure and De Facto Standards

+ + If a feature is unstable (i.e. the spec has not yet stabilized), but + + * at least three UAs implement the feature + (or a UA has broken the other rules and shipped for broad use + an unstable or otherwise non-standard feature in a production release), + * and the implementations have rough interoperability, + * and the CSS Working Group has recorded consensus + that this feature should exist and be released, + + implementers may ship that feature unprefixed in broad-release builds. + Rough interoperability is satisfied by a subjective judgment + that even though there may be differences, + the implementations are sufficiently similar + to be used in production websites for a substantial number of use cases. + +

Note that the CSSWG must still be consulted to ensure coordination across vendors + and to ensure coherency review by the CSS experts from each vendor. + Note also that rough interoperability still usually means + painful lack of interop in edge (or not-so-edge) cases, + particularly because details have not been ironed out through the standards review process. + +

+ Why? + If a feature is sufficiently popular that three or more browsers have implemented it before it's finished standardization, + this clause allows releasing the pressure to ship. + Also, if a feature has already escaped into the wild and sites have started depending on it, + pretending it's still “experimental” doesn't help anyone. + Allowing others to ship unprefixed recognizes that the feature is now de facto standardized + and encourages authors to write cross-platform code. +
+ +
+Vendor-prefixing Unstable Features
+ +

When exposing such a standards-track unstable feature to the Web in a production release, + implementations should support both vendor-prefixed and unprefixed syntaxes + for the feature. + Once the feature has stabilized and the implementation is updated to match interoperable behavior, + support for the vendor-prefixed syntax should be removed. + +

+ Why? + This is recommended so that authors can use the unprefixed syntax to target all implementations, + but when necessary, can target specific implementations + to work around incompatibilities among implementations + as they get ironed out through the standards/bugfixing process. + + The lack of a phase + where only the prefixed syntax is supported + greatly reduces the risk of stylesheets + being written with only the vendor-prefixed syntax. + This in turn allows UA vendors to retire + their prefixed syntax once the feature is stable, + with a lower risk of breaking existing content. + It also reduces the need occasionally felt by some vendors + to support a feature with the prefix of another vendor, + due to content depending on that syntax. +
+ + Anyone promoting unstable features to authors + should document them using their standard unprefixed syntax, + and avoid encouraging the use of the vendor-prefixed syntax + for any purpose other than working around implementation differences. + +
+Preserving the Openness of CSS
+ + In order to preserve the open nature of CSS as a technology, + vendors should make it possible for other implementors + to freely implement any features that they do ship. + To this end, they should provide spec-editing and testing resources + to complete standardization of such features, + and avoid other obstacles (e.g., platform dependency, licensing restrictions) + to their competitors shipping the feature. + +

Implementations of CR-level Features

+ + Once a specification reaches the Candidate Recommendation stage, + implementers should release an unprefixed implementation + of any CR-level feature they can demonstrate + to be correctly implemented according to spec, + and should avoid exposing a prefixed variant of that feature. + + To establish and maintain the interoperability of CSS across + implementations, the CSS Working Group requests that non-experimental + CSS renderers submit an implementation report (and, if necessary, the + testcases used for that implementation report) to the W3C before + releasing an unprefixed implementation of any CSS features. Testcases + submitted to W3C are subject to review and correction by the CSS + Working Group. + + Further information on submitting testcases and implementation reports + can be found from on the CSS Working Group's website at + http://www.w3.org/Style/CSS/Test/. + Questions should be directed to the + public-css-testsuite@w3.org + mailing list. + +

+Safe to Release pre-CR Exceptions

+ + The following features have been explicitly and proactively cleared + by the CSS Working Group for broad release + prior to the spec reaching Candidate Recommendation. + See [[#experimental]]. + + + + The following features have been explicitly and retroactively cleared + by the CSS Working Group for broad release + prior to the spec reaching Candidate Recommendation: + + +

Indices

+ +These sections are non-normative. + +

Terms Index

+ + + +

Selector Index

+ + + +

+At-Rule Index

+ + + +

Property Index

+ + + +

Values Index

+ + + +Acknowledgements {#acks} +======================== + +Special thanks to Florian Rivoal for creating the initial draft of the [[#experimental]] recommendations.