wp-includes/functions.php:2285Determines if a directory is writable.
$pathstringboolfunction wp_is_writable( $path ) { if ( 'Windows' === PHP_OS_FAMILY ) { return win_is_writable( $path ); } return @is_writable( $path );}Introduced in 3.6.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/functions.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.