wp-admin/includes/class-wp-filesystem-ftpext.php:301Changes current directory.
$dirstringbool public function chdir( $dir ) { return @ftp_chdir( $this->link, $dir ); }Introduced in 2.5.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-admin/includes/class-wp-filesystem-ftpext.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.