wp-includes/l10n/class-wp-translation-file.php:217Returns the plural form for a given number.
$numberintint public function get_plural_form( int $number ): int { if ( ! $this->parsed ) { $this->parse_file(); } if ( null === $this->plural_forms && isset( $this->headers['plural-forms'] ) ) { $expression = $this->get_plural_expression_from_header( $this->headers['plural-forms'] ); $this->plural_forms = $this->make_plural_form_function( $expression ); } if ( is_callable( $this->plural_forms ) ) { /** * Plural form. * * @var int $result Plural form. */ $result = call_user_func( $this->plural_forms, $number ); return $result; } // Default plural form matches English, only "One" is considered singular. return ( 1 === $number ? 0 : 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.