Controls whether or not existing files will be overwritten when files of the same name are uploaded.
Possible Values: true/false
When not specified or set to 'false', existing files will not be overwritten by the file upload widget. If any of the file names being uploaded already exist in the target directory, a validation error message will display next to the file upload widget and no files will be uploaded.
When set to 'true', any file names already existing in the target directory will be overwritten by the uploaded files.