function _orphans (options) {
  options.hash.memberof = undefined
  return _identifiers(options).filter(function (identifier) {
    if (identifier.kind === 'external') {
      return identifier.description && identifier.description.length > 0
    } else {
      return true
    }
  })
}
Returns an array of the top-level elements which have no parents. Output only includes externals which have a description.
@returns {array}
@static
@category Returns list