Parameter Name:  FEATURE
  Purpose:  To specify a feature or features of a conference or
  broadcast system.
  Format Definition:  This property parameter is defined by the
  following notation:
  featureparam = "FEATURE" "=" featuretext *("," featuretext)
  featuretext  =  ("AUDIO" /     ; Audio capability
  "CHAT" /      ; Chat or instant messaging
  "FEED" /      ; Blog or Atom feed
  "MODERATOR" / ; Moderator dial-in code
  "PHONE" /     ; Phone conference
  "SCREEN" /    ; Screen sharing
  "VIDEO" /     ; Video capability
  x-name /      ; Experimental type
  iana-token)   ; Other IANA registered type
  Description:  This property parameter MAY be specified on the
  "CONFERENCE" property.  Multiple values can be specified.  The
  "MODERATOR" value is used to indicate that the property value is
  specific to the owner/initiator of the conference and contains a
  URI that "activates" the system (e.g., a "moderator" access code
  for a phone conference system that is different from the "regular"
  access code).
  Example:
  CONFERENCE;VALUE=URI;FEATURE=AUDIO:rtsp://audio.example.com/
  event
  CONFERENCE;VALUE=URI;FEATURE=AUDIO,VIDEO:http://video-chat.exam
  ple.com/;group-id=1234