Title: WP_Style_Engine_CSS_Rules_Store::add_rule
Published: November 2, 2022
Last modified: February 24, 2026

---

# WP_Style_Engine_CSS_Rules_Store::add_rule( string $selector, string $rules_group ): 󠀁[WP_Style_Engine_CSS_Rule](https://developer.wordpress.org/reference/classes/wp_style_engine_css_rule/)󠁿|void

## In this article

 * [Description](https://developer.wordpress.org/reference/classes/wp_style_engine_css_rules_store/add_rule/?output_format=md#description)
 * [Parameters](https://developer.wordpress.org/reference/classes/wp_style_engine_css_rules_store/add_rule/?output_format=md#parameters)
 * [Return](https://developer.wordpress.org/reference/classes/wp_style_engine_css_rules_store/add_rule/?output_format=md#return)
 * [Source](https://developer.wordpress.org/reference/classes/wp_style_engine_css_rules_store/add_rule/?output_format=md#source)
 * [Related](https://developer.wordpress.org/reference/classes/wp_style_engine_css_rules_store/add_rule/?output_format=md#related)
 * [Changelog](https://developer.wordpress.org/reference/classes/wp_style_engine_css_rules_store/add_rule/?output_format=md#changelog)

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

Gets a [WP_Style_Engine_CSS_Rule](https://developer.wordpress.org/reference/classes/wp_style_engine_css_rule/)
object by its selector.

## 󠀁[Description](https://developer.wordpress.org/reference/classes/wp_style_engine_css_rules_store/add_rule/?output_format=md#description)󠁿

If the rule does not exist, it will be created.

## 󠀁[Parameters](https://developer.wordpress.org/reference/classes/wp_style_engine_css_rules_store/add_rule/?output_format=md#parameters)󠁿

 `$selector`stringrequired

The CSS selector.

`$rules_group`stringrequired

A parent CSS selector in the case of nested CSS, or a CSS nested @rule, such as `
@media (min-width: 80rem)` or `@layer module`.

## 󠀁[Return](https://developer.wordpress.org/reference/classes/wp_style_engine_css_rules_store/add_rule/?output_format=md#return)󠁿

 [WP_Style_Engine_CSS_Rule](https://developer.wordpress.org/reference/classes/wp_style_engine_css_rule/)
|void Returns a [WP_Style_Engine_CSS_Rule](https://developer.wordpress.org/reference/classes/wp_style_engine_css_rule/)
object, or void if the selector is empty.

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

    ```php
    public function add_rule( $selector, $rules_group = '' ) {
    	$selector    = $selector ? trim( $selector ) : '';
    	$rules_group = $rules_group ? trim( $rules_group ) : '';

    	// Bail early if there is no selector.
    	if ( empty( $selector ) ) {
    		return;
    	}

    	if ( ! empty( $rules_group ) ) {
    		if ( empty( $this->rules[ "$rules_group $selector" ] ) ) {
    			$this->rules[ "$rules_group $selector" ] = new WP_Style_Engine_CSS_Rule( $selector, array(), $rules_group );
    		}
    		return $this->rules[ "$rules_group $selector" ];
    	}

    	// Create the rule if it doesn't exist.
    	if ( empty( $this->rules[ $selector ] ) ) {
    		$this->rules[ $selector ] = new WP_Style_Engine_CSS_Rule( $selector );
    	}

    	return $this->rules[ $selector ];
    }
    ```

[View all references](https://developer.wordpress.org/reference/files/wp-includes/style-engine/class-wp-style-engine-css-rules-store.php/)
[View on Trac](https://core.trac.wordpress.org/browser/tags/6.9.4/src/wp-includes/style-engine/class-wp-style-engine-css-rules-store.php#L132)
[View on GitHub](https://github.com/WordPress/wordpress-develop/blob/6.9.4/src/wp-includes/style-engine/class-wp-style-engine-css-rules-store.php#L132-L154)

## 󠀁[Related](https://developer.wordpress.org/reference/classes/wp_style_engine_css_rules_store/add_rule/?output_format=md#related)󠁿

| Uses | Description | 
| [WP_Style_Engine_CSS_Rule::__construct()](https://developer.wordpress.org/reference/classes/wp_style_engine_css_rule/__construct/)`wp-includes/style-engine/class-wp-style-engine-css-rule.php` |

Constructor.

  |

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

| Version | Description | 
| [6.6.0](https://developer.wordpress.org/reference/since/6.6.0/) | Added the $rules_group parameter. | 
| [6.1.0](https://developer.wordpress.org/reference/since/6.1.0/) | Introduced. |

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