wp-includes/l10n/class-wp-translation-file.php:250Returns the plural forms expression as a tuple.
$headerstringstring protected function get_plural_expression_from_header( string $header ): string { if ( preg_match( '/^\s*nplurals\s*=\s*(\d+)\s*;\s+plural\s*=\s*(.+)$/', $header, $matches ) ) { return trim( $matches[2] ); } return 'n != 1'; }Introduced in 6.5.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/l10n/class-wp-translation-file.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.