You're seeing just the function
open, go back to SlackWeb.Mpim module for more information.
This method opens a multiparty direct message.
users- Comma separated lists of users. The ordering of the users is preserved whenever a MPIM group is returned.
Errors the API can return:
not_enough_users- Needs at least 2 users to open
too_many_users- Needs at most 8 users to open