wp-includes/class-wp-theme-json.php:1529Processes the CSS, to apply nesting.
$cssstring$selectorstringstring public static function process_blocks_custom_css( $css, $selector ) { $processed_css = ''; if ( empty( $css ) ) { return $processed_css; } // Split CSS nested rules. $parts = explode( '&', $css ); foreach ( $parts as $part ) { if ( empty( $part ) ) { continue; } $is_root_css = ( ! str_contains( $part, '{' ) ); if ( $is_root_css ) { // If the part doesn't contain braces, it applies to the root level. $processed_css .= ':root :where(' . trim( $selector ) . '){' . trim( $part ) . '}'; } else { // If the part contains braces, it's a nested CSS rule. $part = explode( '{', str_replace( '}', '', $part ) ); if ( count( $part ) !== 2 ) { continue; } $nested_selector = $part[0]; $css_value = $part[1]; /* * Handle pseudo elements such as ::before, ::after etc. Regex will also * capture any leading combinator such as >, +, or ~, as well as spaces. * This allows pseudo elements as descendants e.g. `.parent ::before`. */ $matches = array(); $has_pseudo_element = preg_match( '/([>+~\s]*::[a-zA-Z-]+)/', $nested_selector, $matches ); $pseudo_part = $has_pseudo_element ? $matches[1] : ''; $nested_selector = $has_pseudo_element ? str_replace( $pseudo_part, '', $nested_selector ) : $nested_selector; // Finalize selector and re-append pseudo element if required. $part_selector = str_starts_with( $nested_selector, ' ' ) ? static::scope_selector( $selector, $nested_selector ) : static::append_to_selector( $selector, $nested_selector ); $final_selector = ":root :where($part_selector)$pseudo_part"; $processed_css .= $final_selector . '{' . trim( $css_value ) . '}'; } } return $processed_css; }Introduced in 6.2.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-theme-json.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.