Note that this reference documentation is identical to the help that is displayed in MATLAB when you type “help ft_warning”.

  FT_WARNING prints a warning message on screen, depending on the verbosity 
  settings of the calling high-level FieldTrip function. This function works
  similar to the standard WARNING function, but also features the "once" mode.
 
  Use as
    ft_warning(...)
  with arguments similar to fprintf, or
    ft_warning(msgId, ...)
  with arguments similar to warning.
 
  You can switch of all warning messages using
    ft_warning off
  or for specific ones using
    ft_warning off msgId
 
  To switch them back on, you would use 
    ft_warning on
  or for specific ones using
    ft_warning on msgId
  
  Warning messages are only printed once per timeout period using
    ft_warning timeout 60
    ft_warning once
  or for specific ones using
    ft_warning once msgId
 
  You can see the most recent messages and identifier using
    ft_warning last
 
  You can query the current on/off/once state for all messages using
    ft_warning query
 
  See also FT_ERROR, FT_WARNING, FT_NOTICE, FT_warning, FT_DEBUG, ERROR, WARNING