from Versions.txt under version 5.9
Code:
37.mIRC now supports the numeric 005 tokens: CHANTYPES=# and
   PREFIX=(ohv)@%+ and can handle a dynamic set of channel and
   nick prefixes.

   mIRC assumes that @ is supported on all networks, any mode
   left of @ is assumed to have at least equal power to @, and
   any mode right of @ has less power.

   mIRC has internal support for @%+ modes.

   $nick() can now handle all mode letters listed in PREFIX.

   Also added support for CHANMODES=A,B,C,D token (not currently
   supported by any servers), which lists all modes supported
   by a channel, where:

     A = modes that take a parameter, and add or remove nicks
         or addresses to a list, such as +bIe for the ban,
         invite, and exception lists.

     B = modes that change channel settings, but which take
         a parameter when they are set and unset, such as
         +k key, and -k key.

     C = modes that change channel settings, but which take
         a parameter only when they are set, such as +l N,
         and -l.

     D = modes that change channel settings, such as +imnpst
         and take no parameters.

   All unknown/unlisted modes are treated as type D.

   When not connected to a server, mIRC uses default values
   of CHANTYPES=#& PREFIX=(ohv)@%+ CHANMODES=bIe,k,l

   Also added identifiers $chantypes $prefix $chanmodes.

   Notes:

   1. mIRC doesn't support @ or $ as a channel prefix, or $ as
      a nickname prefix, these are used internally by mIRC.

   2. Ircd coders should be aware that prefixes can change
      the way an IRC client behaves.

      eg. If a server uses the same prefixes for channels and
      nicknames, this could cause certain features in mIRC
      to behave oddly, eg. scripts, hotlinks, tab completion,
      etc. which, depending on the prefix, provide a different
      behaviour or interface in non-context situations.