wp-includes/style-engine/class-wp-style-engine-css-rule.php:123Sets the rules group.
$rules_groupstringWP_Style_Engine_CSS_Rule public function set_rules_group( $rules_group ) { $this->rules_group = $rules_group; return $this; }Introduced in 6.6.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/style-engine/class-wp-style-engine-css-rule.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.