# File lib/chef-config/config.rb, line 788
    def self.set_defaults_for_nix
      # Those lists of regular expressions define what chef considers a
      # valid user and group name
      #
      # user/group cannot start with '-', '+' or '~'
      # user/group cannot contain ':', ',' or non-space-whitespace or null byte
      # everything else is allowed (UTF-8, spaces, etc) and we delegate to your O/S useradd program to barf or not
      # copies: http://anonscm.debian.org/viewvc/pkg-shadow/debian/trunk/debian/patches/506_relaxed_usernames?view=markup
      default :user_valid_regex, [ /^[^-+~:,\t\r\n\f\0]+[^:,\t\r\n\f\0]*$/ ]
      default :group_valid_regex, [ /^[^-+~:,\t\r\n\f\0]+[^:,\t\r\n\f\0]*$/ ]
    end