Asks the delegate to validate the URL for a file that the user selected.
- macOS 10.6+
The panel that requests URL validation.
The URL for you to validate.
If an error occurred during validation, the error that occurred.
true if your app can open or save the item at the specified URL. Return
false if you cannot open or save the item.
Save panels call this method when the user clicks the Save button. Open panels call it when the user clicks the Open button. An Open panel calls this method once for each selected filename or directory.