SO answer

fm_elfinder

fm_elfinder:
      locale: %locale%
      editor: ckeditor # other choices are tinymce or simple
      compression: false
      include_assets: true
      fullscreen: true
      connector:
          debug: true # defaults to false
          roots:       # at least one root must be defined <-- roots section
              uploads:
                  driver: LocalFileSystem
                  path: uploads  
                  showhidden: true # <-- showhidden option
                  upload_allow: ['image/png', 'image/jpg', 'image/jpeg']
                  upload_deny: ['all']
                  upload_max_size: 2M