.. hook:: H_TELNET_NEG

  :arg string value: void|mixed <name>(int action, int option [, int * opts ] )
  :arg closure value: void|mixed <closure>(int action, int option [, int * opts ] )

  Optional hook to specifiy how to perform a single telnet negotiation. Hook setting may be any closure or a string. If not set, most telnet options are rejected (read: only a very minimal negotiation takes place).

  The hook is called whenever the driver receives a demand for option negotiation for any option the driver does not handle itself. By default, the driver deals with the following options:

      :macro:`TELOPT_ECHO`:      Echo option
      :macro:`TELOPT_SGA`:       Suppress Go Ahead (nearly always on)
      :macro:`TELOPT_COMPRESS`:  Mud client compression protocol (obsolete)
      :macro:`TELOPT_COMPRESS2`: Mud client compression protocol V2

  For all other telnet options negotiations, this hook is called.

  The hook has then to perform the negotiation using the :efun::`binary_message`.

  Alternatively, if :hook:`H_NOECHO` is set, this hook is called for *all* telnet data received.

  If the setting is a string, it used as the name of an lfun to call in ``this_player()``. Closures are just called, with unbound lambda-closures being bound to ``this_player()`` prior to execution.

  The hook is called for a 'DO/DONT/WILL/WONT <opt>' with the action (DO/DONT/...) as the first, and <opt> as the second argument.

  For example:, if the driver receives the sequence

    IAC SB <opt> <opts>...

  followed by IAC SB/SE, the hook is called with 'SB' as first argument, <opt> as second, and <opts> as an array of integers as third argument.

  .. subtopic:: Negotiations

    An incomplete list of telnet negotiations this hook is called for includes the following:
      SB:               Suboption negotiation
      :macro:`TELOPT_LINEMODE`:  linemode
      :macro:`TELOPT_NAWS`:      window size
      :macro:`TELOPT_TTYPE`:     terminal type
      :macro:`TELOPT_TM`:        timing mark
      :macro:`TELOPT_NEWENV`:    remote environment variables
      :macro:`TELOPT_ENVIRON`:   remote environment variables
      :macro:`TELOPT_XDISPLOC`:  remote X display address
      :macro:`TELOPT_TSPEED`:    terminal speed
      :macro:`TELOPT_BINARY`:    binary data, needed for non-ASCII charsets
      :macro:`TELOPT_EOR`:       TinyFugue prompt marker (together with EOR)

      :macro:`TELOPT_MSP`:       Mud Sound Protocol
      :macro:`TELOPT_MXP`:       Mud Extension Protocol
      :macro:`TELOPT_MSSP`:      Mud Server Status Protocol
      :macro:`TELOPT_GMCP`:      Generic Mud Communication Protocol

  .. history

  .. seealso:: :overview:`hook`, :concept:`telnet`, :hook:`no_echo`