MIgrate file handler 'destination dir' description isn't clear

I spent about an hour trying to decipher the MigrateFile class 'DestinationDir' sub-field, with file migrations failing, even though the files were available. The problem was a misinterpretation of the nature of the field value.

The migrate field description is: "Path within Drupal files directory to store file"

This is not clear. The default value for the sub-field is 'public://'. The variable holds a full Drupal File Scheme uri. Any passed values need to still be a full uri, not a path for inside the files directory (public://[path_inside_files_directory]).

In my case it was hard to determine where the file migration was failing. I had a subfolder for inside the files directory, which as an absolute url the server didn't have the permissions to create.

Perhaps something like this would be more clear: "Drupal path uri to the directory to store file (defaults to public://)"

I am not sure how comfortable most migrators are with the Drupal URI schemes, but I would assume that the level is high, so just seeing the default suggestion would inform that a scheme uri is used.