Title: WP_Style_Engine_Processor
Published: November 2, 2022
Last modified: May 20, 2026

---

# class WP_Style_Engine_Processor {}

## In this article

 * [Methods](https://developer.wordpress.org/reference/classes/wp_style_engine_processor/?output_format=md#methods)
 * [Source](https://developer.wordpress.org/reference/classes/wp_style_engine_processor/?output_format=md#source)
 * [Changelog](https://developer.wordpress.org/reference/classes/wp_style_engine_processor/?output_format=md#changelog)

[ Back to top](https://developer.wordpress.org/reference/classes/wp_style_engine_processor/?output_format=md#wp--skip-link--target)

Core class used to compile styles from stores or collection of CSS rules.

## 󠀁[Methods](https://developer.wordpress.org/reference/classes/wp_style_engine_processor/?output_format=md#methods)󠁿

| Name | Description | 
| [WP_Style_Engine_Processor::add_rules](https://developer.wordpress.org/reference/classes/wp_style_engine_processor/add_rules/) | Adds rules to be processed. | 
| [WP_Style_Engine_Processor::add_store](https://developer.wordpress.org/reference/classes/wp_style_engine_processor/add_store/) | Adds a store to the processor. | 
| [WP_Style_Engine_Processor::combine_rules_selectors](https://developer.wordpress.org/reference/classes/wp_style_engine_processor/combine_rules_selectors/) | Combines selectors from the rules store when they have the same styles. | 
| [WP_Style_Engine_Processor::get_css](https://developer.wordpress.org/reference/classes/wp_style_engine_processor/get_css/) | Gets the CSS rules as a string. |

## 󠀁[Source](https://developer.wordpress.org/reference/classes/wp_style_engine_processor/?output_format=md#source)󠁿

    ```php
    #[AllowDynamicProperties]
    class WP_Style_Engine_Processor {

    	/**
    	 * A collection of Style Engine Store objects.
    	 *
    	 * @since 6.1.0
    	 * @var WP_Style_Engine_CSS_Rules_Store[]
    	 */
    	protected $stores = array();

    	/**
    	 * The set of CSS rules that this processor will work on.
    	 *
    	 * @since 6.1.0
    	 * @var WP_Style_Engine_CSS_Rule[]
    	 */
    	protected $css_rules = array();

    	/**
    	 * Adds a store to the processor.
    	 *
    	 * @since 6.1.0
    	 *
    	 * @param WP_Style_Engine_CSS_Rules_Store $store The store to add.
    	 * @return WP_Style_Engine_Processor Returns the object to allow chaining methods.
    	 */
    	public function add_store( $store ) {
    		if ( ! $store instanceof WP_Style_Engine_CSS_Rules_Store ) {
    			_doing_it_wrong(
    				__METHOD__,
    				__( '$store must be an instance of WP_Style_Engine_CSS_Rules_Store' ),
    				'6.1.0'
    			);
    			return $this;
    		}

    		$this->stores[ $store->get_name() ] = $store;

    		return $this;
    	}

    	/**
    	 * Adds rules to be processed.
    	 *
    	 * @since 6.1.0
    	 * @since 6.6.0 Added support for rules_group.
    	 *
    	 * @param WP_Style_Engine_CSS_Rule|WP_Style_Engine_CSS_Rule[] $css_rules A single, or an array of,
    	 *                                                                       WP_Style_Engine_CSS_Rule objects
    	 *                                                                       from a store or otherwise.
    	 * @return WP_Style_Engine_Processor Returns the object to allow chaining methods.
    	 */
    	public function add_rules( $css_rules ) {
    		if ( ! is_array( $css_rules ) ) {
    			$css_rules = array( $css_rules );
    		}

    		foreach ( $css_rules as $rule ) {
    			$selector    = $rule->get_selector();
    			$rules_group = $rule->get_rules_group();

    			/**
    			 * If there is a rules_group and it already exists in the css_rules array,
    			 * add the rule to it.
    			 * Otherwise, create a new entry for the rules_group.
    			 */
    			if ( ! empty( $rules_group ) ) {
    				if ( isset( $this->css_rules[ "$rules_group $selector" ] ) ) {
    					$this->css_rules[ "$rules_group $selector" ]->add_declarations( $rule->get_declarations() );
    					continue;
    				}
    				$this->css_rules[ "$rules_group $selector" ] = $rule;
    				continue;
    			}

    			// If the selector already exists, add the declarations to it.
    			if ( isset( $this->css_rules[ $selector ] ) ) {
    				$this->css_rules[ $selector ]->add_declarations( $rule->get_declarations() );
    				continue;
    			}
    			$this->css_rules[ $rule->get_selector() ] = $rule;
    		}

    		return $this;
    	}

    	/**
    	 * Gets the CSS rules as a string.
    	 *
    	 * @since 6.1.0
    	 * @since 6.4.0 The Optimization is no longer the default.
    	 *
    	 * @param array $options   {
    	 *     Optional. An array of options. Default empty array.
    	 *
    	 *     @type bool $optimize Whether to optimize the CSS output, e.g. combine rules.
    	 *                          Default false.
    	 *     @type bool $prettify Whether to add new lines and indents to output.
    	 *                          Defaults to whether the `SCRIPT_DEBUG` constant is defined.
    	 * }
    	 * @return string The computed CSS.
    	 */
    	public function get_css( $options = array() ) {
    		$defaults = array(
    			'optimize' => false,
    			'prettify' => defined( 'SCRIPT_DEBUG' ) && SCRIPT_DEBUG,
    		);
    		$options  = wp_parse_args( $options, $defaults );

    		// If we have stores, get the rules from them.
    		foreach ( $this->stores as $store ) {
    			$this->add_rules( $store->get_all_rules() );
    		}

    		// Combine CSS selectors that have identical declarations.
    		if ( true === $options['optimize'] ) {
    			$this->combine_rules_selectors();
    		}

    		// Build the CSS.
    		$css = '';
    		foreach ( $this->css_rules as $rule ) {
    			// See class WP_Style_Engine_CSS_Rule for the get_css method.
    			$css .= $rule->get_css( $options['prettify'] );
    			$css .= $options['prettify'] ? "\n" : '';
    		}
    		return $css;
    	}

    	/**
    	 * Combines selectors from the rules store when they have the same styles.
    	 *
    	 * @since 6.1.0
    	 */
    	private function combine_rules_selectors() {
    		// Build an array of selectors along with the JSON-ified styles to make comparisons easier.
    		$selectors_json = array();
    		foreach ( $this->css_rules as $rule ) {
    			$declarations = $rule->get_declarations()->get_declarations();
    			ksort( $declarations );
    			$selectors_json[ $rule->get_selector() ] = wp_json_encode( $declarations );
    		}

    		// Combine selectors that have the same styles.
    		foreach ( $selectors_json as $selector => $json ) {
    			// Get selectors that use the same styles.
    			$duplicates = array_keys( $selectors_json, $json, true );
    			// Skip if there are no duplicates.
    			if ( 1 >= count( $duplicates ) ) {
    				continue;
    			}

    			$declarations = $this->css_rules[ $selector ]->get_declarations();

    			foreach ( $duplicates as $key ) {
    				// Unset the duplicates from the $selectors_json array to avoid looping through them as well.
    				unset( $selectors_json[ $key ] );
    				// Remove the rules from the rules collection.
    				unset( $this->css_rules[ $key ] );
    			}
    			// Create a new rule with the combined selectors.
    			$duplicate_selectors                     = implode( ',', $duplicates );
    			$this->css_rules[ $duplicate_selectors ] = new WP_Style_Engine_CSS_Rule( $duplicate_selectors, $declarations );
    		}
    	}
    }
    ```

[View all references](https://developer.wordpress.org/reference/files/wp-includes/style-engine/class-wp-style-engine-processor.php/)
[View on Trac](https://core.trac.wordpress.org/browser/tags/7.0/src/wp-includes/style-engine/class-wp-style-engine-processor.php#L15)
[View on GitHub](https://github.com/WordPress/wordpress-develop/blob/7.0/src/wp-includes/style-engine/class-wp-style-engine-processor.php#L15-L181)

## 󠀁[Changelog](https://developer.wordpress.org/reference/classes/wp_style_engine_processor/?output_format=md#changelog)󠁿

| Version | Description | 
| [6.1.0](https://developer.wordpress.org/reference/since/6.1.0/) | Introduced. |

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