Check for valid path

Is it not desirable if the check happens immediately (specify the folder) when you press NEXT , like in windows when the user used invalid letters? The check if the path is correct or not happens when the installation process were started and then, when an incorrect hard drive was entered, comes the message of in invalid hard drive. After that it is not possible to go back, by using the arrow button top left, to specify a correct path / hard drive because the installation process ended automatically.
There should even a check for write-protected folders.