It adds 3 new rules and 1 configuration property.

• Added: languageOptions.directionality configuration property (#8687) (@sw1tch3roo).
• Added: property-layout-mappings rule (#8687) (@sw1tch3roo).
• Added: relative-selector-nesting-notation rule (#8730) (@sw1tch3roo).
• Added: selector-no-deprecated rule (#8694) (@immitsu).

It fixes 4 bugs, including clearer problem messages by removing filler words and leading with the problem. We've also released 1.0.0 of create-stylelint to help with first-time Stylelint setup.

• Fixed: clarity of problem messages (#9199) (@jeddy3).
• Fixed: --print-config CLI flag to hide internal properties (#9194) (@ybiquitous).
• Fixed: function-url-quotes false positives when URLs have modifiers (#8702) (@immitsu).
• Fixed: selector-no-qualifying-type false positives for :has() (#9182) (@romainmenke).

It adds support for extending units in languageOptions, which then apply to rules like declaration-property-value-no-unknown, and fixes 2 bugs.

• Added: support for extending units to languageOptions (#9166) (@jeddy3).
• Fixed: missing ruleMetadata when linting multiple files with overrides (#9154) (@kovsu).
• Fixed: custom-property-no-missing-var-function false positives for timeline-scope and animation-timeline (#9164) (@splincode).

It deprecates two rule options, adds 1 rule option and fixes 7 bugs. We've also released 2.1.0 of our VS Code extension, which adds 8 new requested features, and our first release of the Stylelint Language Server.

• Deprecated: *syntax options from declaration-property-value-no-unknown (#9102) (@ragini-pandey).
• Added: ignoreMediaFeatureNameValues: {} to media-feature-name-value-no-unknown (#8976) (@kovsu).
• Fixed: node_modules not ignored when using codeFilename in Node.js API (#9130) (@adalinesimonian).
• Fixed: Error TS7016 for imported css-tree types (#9133) (@ragini-pandey).
• Fixed: declaration-property-value-keyword-no-deprecated false positives for function arguments (#9116) (@ragini-pandey).
• Fixed: declaration-property-value-no-unknown false positives for calc-size() containing size keyword (#9105) (@hriztam).
• Fixed: no-descending-specificity & no-duplicate-selectors false negatives for equivalent compound selectors (#8977) (@kovsu).
• Fixed: no-invalid-position-declaration false positives for @mixin and @scope (#9120) (@ragini-pandey).
• Fixed: property-no-unknown false negatives for types (#9117) (@Mouvedia).

It adds 2 options to the rules and fixes 7 bugs.

• Added: ignoreAtRules: [] to at-rule-no-vendor-prefix (#9096) (@theacrat).
• Added: ignoreMediaFeatureNames: [] to media-feature-name-no-vendor-prefix (#9097) (@theacrat).
• Fixed: performance of selector cloning rules (#9089) (@jeddy3).
• Fixed: *-empty-line-before performance (#9092) (@jeddy3).
• Fixed: declaration-property-value-no-unknown performance (#9090) (@jeddy3).
• Fixed: no-irregular-whitespace performance (#9091) (@jeddy3).
• Fixed: property-no-unknown false negatives for at-rule descriptors (#9109) (@jeddy3).
• Fixed: property-no-unknown false positives for corner-shape (#9099) (@jeddy3).
• Fixed: property-no-unknown false positives for double-slashed properties (#9099) (@jeddy3).

It fixes 17 bugs. 3 related to supporting calc() in declaration-property-value-no-unknown, and 13 performance ones that make Stylelint a further 3x faster when using the rules in our standard config.

• Fixed: performance of rule sequencing (#9055) (@jeddy3).
• Fixed: *-list performance (#9056) (@jeddy3).
• Fixed: *-notation performance (#9044) (@jeddy3).
• Fixed: declaration-property-max-values performance (#9057) (@jeddy3).
• Fixed: declaration-property-value-keyword-no-deprecated performance (#9058) (@jeddy3).
• Fixed: declaration-property-value-no-unknown false negatives for math functions inside of non-math functions (#9064) (@romainmenke).
• Fixed: declaration-property-value-no-unknown false positives for calc() with mixed operations (#9064) (@romainmenke).
• Fixed: declaration-property-value-no-unknown performance (#9062) (@jeddy3).
• Fixed: declaration-property-value-no-unknown reported ranges for multiple math functions (#9064) (@romainmenke).
• Fixed: length-zero-no-unit performance (#9046) (@jeddy3).
• Fixed: named-grid-areas-no-invalid false positives for mix of tabs and spaces (#9039) (@adalinesimonian).
• Fixed: no-unknown-custom-media performance (#9059) (@jeddy3).
• Fixed: selector-max-* performance (#9042) (@jeddy3).
• Fixed: shorthand-property-no-redundant-values performance (#9047) (@jeddy3).
• Fixed: syntax-string-no-invalid performance (#9061) (@jeddy3).
• Fixed: time-min-milliseconds performance (#9060) (@jeddy3).
• Fixed: value-keyword-case performance (#9048) (@jeddy3).

It fixes 7 bugs, including 5 performance ones that make Stylelint 7x faster and use 3x less memory on larger codebases such as design systems and monorepos. We also restructured our docs to create a contributor guide. If you'd like to help out and contribute to Stylelint, that's the place to start.

• Fixed: performance of config augmentation and module imports (#9021) (@adalinesimonian).
• Fixed: performance of config override matching (#9023) (@adalinesimonian).
• Fixed: performance of config resolution (#9033) (@adalinesimonian).
• Fixed: performance of rule resolution (#9022) (@adalinesimonian).
• Fixed: declaration-property-value-no-unknown false negatives for math functions (#9011) (@ragini-pandey).
• Fixed: no-duplicate-selectors false negatives for matching escaped selectors (#8953) (@bjnewman).
• Fixed: no-invalid-position-at-import-rule false negatives for layers with blocks (#9026) (@romainmenke).

It fixes 2 bugs.

• Fixed: resolution of configs, plugins, processors, and custom syntaxes in Yarn PnP environments (#9010) (@adalinesimonian).
• Fixed: lightness-notation autofix for decimals (#9009) (@IlyaSemenov).

It fixes 5 bugs and adds the display-notation rule. Before we turn it on in our standard config, we'd like to hear the community's thoughts on which options to use.

• Added: display-notation rule (#8981) (@romainmenke).
• Fixed: GlobbyOptions TypeScript errors (#8992) (@zalishchuk).
• Fixed: hue-degree-notation false negatives and positives for relative colors (#8985) (@jamesnw).
• Fixed: lightness-notation false negatives for relative colors (#8987) (@jamesnw).
• Fixed: selector-type-no-unknown false positives for geolocation and usermedia (#9004) (@Mouvedia).
• Fixed: selector-type-no-unknown false positives for rb, rtc and menuitem (#8972) (@Mouvedia).

It contains 14 breaking changes, which we've detailed in the migrating to 17.0.0 guide. Additionally, it adds 3 options to the rules and fixes 9 bugs. We've also released compatible versions of our shared config, Visual Studio Code extension, Node.js Rule Tester and Jest preset.

• Removed: CommonJS Node.js API (#8859) (@jeddy3).
• Removed: output property in the Node.js API returned resolved object (#8878) (@jeddy3).
• Removed: support for Node.js less than 20.19.0 (#8867) (@jeddy3).
• Removed: GitHub formatter (#8888) (@jeddy3).
• Removed: resolveNestedSelectors option from selector-class-pattern (#8931) (@jeddy3).
• Removed: checkContextFunctionalPseudoClasses option from selector-max-id (#8913) (@jeddy3).
• Changed: default fix mode to strict (#8889) (@jeddy3).
• Changed: report to be consistent and predictable in how it handles the provided position arguments (#8217) (@romainmenke).
• Changed: selector-max-* syntax rules for standard CSS nesting and modern functional pseudo-classes (#8913) (@jeddy3).
• Changed: *-specificity semantic rules for standard CSS nesting (#8913) (@jeddy3).
• Changed: no-duplicate-selectors and selector-no-qualifying-type for standard CSS nesting (#8913) (@jeddy3).
• Changed: *-list rules to have consistent behaviour for vendor prefixes and case (#8912) (@jeddy3).
• Changed: *-no-vendor-prefix rules to have consistent behaviour for their ignore*: [] secondary options (#8924) (@jeddy3).
• Changed: declaration-property-max-values rule to have consistent behaviour for vendor prefixes (#8926) (@jeddy3).
• Added: except: ["after-block"] to custom-property-empty-line-before (#8921) (@kovsu).
• Added: except: ["after-block"] to declaration-empty-line-before (#8910) (@kovsu).
• Added: ignoreSelectors: [] to no-duplicate-selectors (#8883) (@kovsu).
• Fixed: Windows drive letter casing inconsistencies when matching patterns against file paths (#8941) (@adalinesimonian).
• Fixed: CLI help to include TypeScript config files (#8908) (@kovsu).
• Fixed: at-rule-descriptor-no-unknown false positives for declarations within feature-value-blocks (#8868) (@kovsu).
• Fixed: declaration-block-no-redundant-longhand-properties false negatives for short and long combinations (#8892) (@nathannewyen).
• Fixed: media-feature-name-no-unknown false positives for namespaced dollar variables and range context queries (#8890) (@kovsu).
• Fixed: nesting-selector-no-missing-scoping-root false positives for CSS-in-JS (#8905) (@kovsu).
• Fixed: no-invalid-position-declaration false negatives for embedded blocks (#8907) (@kovsu).
• Fixed: selector-no-qualifying-type false negatives for :is/where() (#8940) (@romainmenke).
• Fixed: selector-type-no-unknown false positives for MathML 4 tags (#8874) (@jeddy3).