This setting limits uploaded file names to a specified regular expression (e.g. ^[0-9].*$ will only allow filenames starting with a number). Your chosen settings will also apply to all of this folder's subfolders by default, unless you override the setting.

When you have a workflow that requires both speed and accuracy of your staff users, and exists within the added complexity of a large folder tree, you can dramatically increase accuracy, making sure that the right files end up in the right folders, by setting regular expression rules to prevent files that do not fit the pattern from being uploaded.

Note that moving or copying folders to destination folders with filename restrictions, such as limiting uploaded files to regular expressions, is not allowed.

Overriding Settings in Subfolders or Excluding Subfolders Entirely

You can override or exclude this setting entirely for subfolders. Users with administrator privileges can customize the restrictions independently of the parent folder. To exclude or override a subfolder from the parent's file name restrictions, an admin with adequate privileges can navigate to the subfolder's settings and select the option Limit uploaded files to regular expression to set unique regular expression for that folder or override the parent folder's settings.