WordPress at a glance
function is not described

win_is_writable() WP 2.8.0

Workaround for Windows bug in is_writable() function

PHP has issues with Windows ACL's for determine if a directory is writable or not, this works around them by checking the ability to open files rather than relying upon PHP to interprate the OS ACL.

No Hooks.

Return

true/false. Whether the path is writable.

Usage

win_is_writable( $path );
$path(string) (required)
Windows path to check for write-ability.

Code of win is writable: wp-includes/functions.php VER 5.0.3

<?php
function win_is_writable( $path ) {

	if ( $path[strlen( $path ) - 1] == '/' ) { // if it looks like a directory, check a random file within the directory
		return win_is_writable( $path . uniqid( mt_rand() ) . '.tmp');
	} elseif ( is_dir( $path ) ) { // If it's a directory (and not a file) check a random file within the directory
		return win_is_writable( $path . '/' . uniqid( mt_rand() ) . '.tmp' );
	}
	// check tmp file for read/write capabilities
	$should_delete_tmp_file = !file_exists( $path );
	$f = @fopen( $path, 'a' );
	if ( $f === false )
		return false;
	fclose( $f );
	if ( $should_delete_tmp_file )
		unlink( $path );
	return true;
}