WP_Style_Engine

Last updated: February 12, 2026

Core class for parsing block styles and compiling CSS. This is a low-level internal API.

Source: wp-includes/style-engine/class-wp-style-engine.php
Since: 6.1.0
Access: Private (use wp_style_engine_get_styles() instead)

Note: This class is final and should not be extended. It is for internal Core usage and may have breaking changes. Use the public functions in style-engine.php instead.

Constants

BLOCK_STYLE_DEFINITIONS_METADATA

Style definitions containing instructions for parsing and outputting valid Gutenberg styles from block attributes.

const BLOCK_STYLE_DEFINITIONS_METADATA = array(
    'background' => array( /* ... */ ),
    'color'      => array( /* ... */ ),
    'border'     => array( /* ... */ ),
    'shadow'     => array( /* ... */ ),
    'dimensions' => array( /* ... */ ),
    'spacing'    => array( /* ... */ ),
    'typography' => array( /* ... */ ),
);

Definition Structure

Key	Type	Description
`classnames`	array	Classnames to return; key is pattern, value is `true` or property key for slug substitution
`css_vars`	array	CSS var patterns for preset conversion (e.g., `--wp--preset--color--$slug`)
`property_keys`	array	CSS properties (`default` and optionally `individual` for box-model styles)
`path`	array	Path to style value in block style object
`value_func`	callable	Custom function to generate CSS declarations

Methods

parse_block_styles()

Returns classnames and CSS based on values in a styles object.

public static function parse_block_styles( array $block_styles, array $options ): array

Parameters

Parameter	Type	Description
`$block_styles`	array	The style object
`$options`	array	Configuration options

Options

Key	Type	Default	Description
`convert_vars_to_classnames`	bool	`false`	Skip converting `var:preset\|*` to CSS vars
`selector`	string	—	CSS selector (not used in parsing, passed through)

Returns

Key	Type	Description
`classnames`	array	Array of CSS class names
`declarations`	array	Associative array of CSS property => value

compile_css()

Returns compiled CSS from CSS declarations.

public static function compile_css( array $css_declarations, string $css_selector ): string

Parameters

Parameter	Type	Description
`$css_declarations`	array	Associative array of CSS definitions
`$css_selector`	string	CSS selector; if empty, returns declarations only

Returns

Compiled CSS string. If selector is provided, returns full rule: $selector { declarations }. Otherwise, returns concatenated declarations.

compile_stylesheet_from_css_rules()

Returns compiled stylesheet from CSS rule objects.

public static function compile_stylesheet_from_css_rules( 
    WP_Style_Engine_CSS_Rule[] $css_rules, 
    array $options = array() 
): string

Parameters

Parameter	Type	Description
`$css_rules`	array	Array of `WP_Style_Engine_CSS_Rule` objects
`$options`	array	Configuration options

Options

Key	Type	Default	Description
`context`	string\|null	—	Store name
`optimize`	bool	`false`	Combine rules with identical declarations
`prettify`	bool	`SCRIPT_DEBUG`	Add formatting

Returns

Compiled CSS string.

store_css_rule()

Stores a CSS rule in a named store for later retrieval.

public static function store_css_rule( 
    string $store_name, 
    string $css_selector, 
    array $css_declarations, 
    string $rules_group = '' 
): void

Since: 6.1.0
Since: 6.6.0 Added $rules_group parameter

Parameters

Parameter	Type	Description
`$store_name`	string	Store key (e.g., `block-supports`)
`$css_selector`	string	CSS selector
`$css_declarations`	array	CSS property => value pairs
`$rules_group`	string	Parent selector or @rule (e.g., `@media (min-width: 80rem)`)

get_store()

Returns a store by its name.

public static function get_store( string $store_name ): ?WP_Style_Engine_CSS_Rules_Store

Parameters

Parameter	Type	Description
`$store_name`	string	Store key

Returns

WP_Style_Engine_CSS_Rules_Store instance, or null if invalid.

Protected Methods

get_slug_from_preset_value()

Extracts the slug in kebab-case from a preset string.

protected static function get_slug_from_preset_value( string $style_value, string $property_key ): string

Parameters

Parameter	Type	Description
`$style_value`	string	CSS preset value (e.g., `var:preset\|color\|heavenlyBlue`)
`$property_key`	string	Property key to match (e.g., `color`)

Returns

Slug in kebab-case (e.g., heavenly-blue), or empty string if not found.

get_css_var_value()

Generates a CSS var string from a preset string.

protected static function get_css_var_value( string $style_value, array $css_vars ): string

Parameters

Parameter	Type	Description
`$style_value`	string	Preset value (e.g., `var:preset\|color\|someSlug`)
`$css_vars`	array	CSS var patterns (e.g., `array( 'color' => '--wp--preset--color--$slug' )`)

Returns

CSS var (e.g., var(--wp--preset--color--some-slug)), or empty string.

is_valid_style_value()

Checks whether a style value is valid.

protected static function is_valid_style_value( mixed $style_value ): bool

Returns

true if value is '0' or non-empty; false otherwise.

get_classnames()

Returns classnames from a style value and definition.

protected static function get_classnames( string $style_value, array $style_definition ): array

Parameters

Parameter	Type	Description
`$style_value`	string	Raw style value or preset
`$style_definition`	array	Style definition from `BLOCK_STYLE_DEFINITIONS_METADATA`

Returns

Array of CSS class names.

get_css_declarations()

Returns CSS declarations from a style value.

protected static function get_css_declarations( 
    mixed $style_value, 
    array $style_definition, 
    array $options = array() 
): array

Parameters

Parameter	Type	Description
`$style_value`	mixed	Raw style value
`$style_definition`	array	Style definition
`$options`	array	Options including `convert_vars_to_classnames`

Returns

Associative array of CSS declarations.

get_individual_property_css_declarations()

Parser for individual property declarations (e.g., border-top-color).

protected static function get_individual_property_css_declarations( 
    array $style_value, 
    array $individual_property_definition, 
    array $options = array() 
): array

Handles styles like:

border-{top|right|bottom|left}-{color|width|style}
border-image-{outset|source|width|repeat|slice}

get_url_or_value_css_declaration()

Parser for URL-based style values (e.g., background-image).

protected static function get_url_or_value_css_declaration( 
    mixed $style_value, 
    array $style_definition 
): array

Since: 6.4.0

Returns

If value contains url key, returns array( 'background-image' => "url('...')" ).

WP_Style_Engine

Constants

BLOCK_STYLE_DEFINITIONS_METADATA

Definition Structure

Methods

parse_block_styles()

Parameters

Options

Returns

compile_css()

Parameters

Returns

compile_stylesheet_from_css_rules()

Parameters

Options

Returns

store_css_rule()

Parameters

get_store()

Parameters

Returns

Protected Methods

get_slug_from_preset_value()

Parameters

Returns

get_css_var_value()

Parameters

Returns

is_valid_style_value()

Returns

get_classnames()

Parameters

Returns

get_css_declarations()

Parameters

Returns

get_individual_property_css_declarations()

get_url_or_value_css_declaration()

Returns

More in Style Engine

WP_Style_Engine_CSS_Declarations

WP_Style_Engine_CSS_Rule

WP_Style_Engine_Processor