gnus: Group Mode Line Specification

 
 2.1.2 Group Mode Line Specification
 -----------------------------------
 
 The mode line can be changed by setting ‘gnus-group-mode-line-format’
 (SeeMode Line Formatting).  It doesn’t understand that many format
 specifiers:
 
 ‘S’
      The native news server.
 ‘M’
      The native select method.