Now, before I start to get into linetype actions and such, I'd just like 
to make sure you understand how linetype actions work.  Almost all 
linetypes produce an action.  All actions affect a sector.  Sometimes 
the sector affected is determined by a fixed rule, such as some with doors.  
The rest are determined through the use of a trigger id.

Both lines and sectors may have a trigger id.  The line is the source of 
an action, while the sector is what actually performs the action.  In 
order to know what line affects what sector, a common trigger id is given
to both the line and the sector.  This id number can be any number of your
choosing.  It doesn't have to be a certain number or anything.  It is 
simply used to uniquely identify seperate actions.  It's like a serial
number.

Because this trigger id method is used, instead of lines and sectors
directly referencing each other, it is possible to have multiple lines
tied to multiple sectors.  For example, having 3 different switches on a
wall all do the same thing to the same sector.  Or, different things to
the same sector.  Or, you can have a single switch open 10 different
doors at once, etc.

Ok, all linetypes have a code that describes the characteristics of that 
linetype.  This includes how a line is activated, if it is reusable or 
only single-use, if a trigger id is required, and if this linetype is 
new and only usable in Doom v1.4 or higher (Doom II started at v1.666, so
it can use all these types).

The code is 4 characters long.  Each character describes something 
different.

   a) The first character can be ' ' or '*'.  A '*' means it is only 
      available in Doom v1.4 or above.  Using a linetype like this means 
      that it can only be played on Doom v1.4 or higher.

   b) The second character can be ' ' or 'n'.  An 'n' means that it 
      doesn't require a trigger id, and using a trigger id that isn't 
      zero may cause problems.

   c) The third character can be 'S', 'W', 'G' or '-'.
        
        'S': Switch activated linetype.  This means that the spacebar 
             (or open mouse button/joystick button, etc) needs to be 
             pressed while standing in front of the line to activate it.

        'W': Walk over activated linetype.  A player, monster, or 
             sometimes rocket/fireball will activate this linetype when it
             crosses this line.

        'G': Gun or other weapon activated linetype.  You need to shoot 
             this line to activate it.  Other weapons that will work 
             include your fist, chainsaw, chaingun, rocket launcher, 
             fireballs, etc.

        '-': This means that the line can't be activated.  Of course, no 
             action ever occurs either.

   d) The fourth character can be 'R' or '1'.  'R' means it is a 
      reusable linetype, and '1' means it can only be used once.

Note that most, if not all, linetypes are activated from the right 
side.  Thus, switches on walls should be on the right side, and walk 
over linetypes should be crossed over from the right side over to the 
left side to activate.  Keep this in mind.  If a line only has textures 
on one side, the textured side must be on the right side, and DMapEdit 
will always flip the line to insure this.  This may interfere with your 
line activation.  If you want to flip the line around in this case, put 
texture on the other side in the upper or lower texture slot and you 
should be able to flip it around then.

Door with a 'n' (no trigger id required) type will affect the sector on 
the left side of the line.  These are used for door that you walk up to 
and open manually with the spacebar.  Of course, this type should never 
be used on a single sided line.

Teleport line types will teleport a player or monster elsewhere when 
they cross the line.  These lines are usually arranged in a square shape 
around a pentagon-style floored sector.  There should only be one sector 
tied to line/lines.  Having multiple sector won't allow for 'random 
destinations'.  When teleported, the player/moster arrives in the sector 
tied to the line, and more specifically, at a teleporter arrival point, 
which is a Thing.  If you forget to add one to the sector, or have more 
than one, Doom will crash.  Also, the facing direction of this arrival 
Thing is the direction the player/monster will be facing when they are 
finsihed teleporting.

Linetype #9: 'Equalize donut sector floors', is a rather complex
action.  It will actually effect 2 different sectors, and these
sectors should normally be set up in a donut fashion, like so:

                +-----------+
                |     2     |
                |  +-----+  | 3
                |  |     |  |
                | 2|  1  |2 |
              3 |  |     |  |
                |  +-----+  |
                |     2     |
                +-----------+

The base sector (the one the line is tied to via trigger id) in this 
case is sector #1.  It, and the next one out (sector #2) will change
their floor heights to match the 3rd one out's (sector #3).  They can go 
either direction, and can move in opposite directions even.  
Furthermore, both sectors (1 & 2) will change their floor texture and 
sector type to match the template sector's (sector #3).  Sounds 
complicated, eh?  An example of this linetype is in E1M2, where you get 
the chainsaw.  You flip a switch on the wall, and the pillar the 
chainsaw is on comes down, while the donut sector around it raises and 
changes texture.  

Linetype #49: Start normal crushing ceiling, works properly in Doom v1.6 
and above.  However, before that, it acts like a crushing ceiling but 
doesn't do any damage.  This was a bug that id fixed, apparently.

Lift always work work the same way.  They first lower to the next-lower 
floor height, wait for about 2 seconds, and then raise back to their 
original starting height and stay there until activated again.  You 
cannot make a lift raise first and then lower.  Sorry, this is just a 
limitation id created.  I can't do anything about it.
