transition_kind Indicates the next room transition. You can use the following builtin values

0 = no effect
1 = Create from left
2 = Create from right
3 = Create from top
4 = Create from bottom
5 = Create from center
6 = Shift from left
7 = Shift from right
8 = Shift from top
9 = Shift from bottom
10 = Interlaced from left
11 = Interlaced from right
12 = Interlaced from top
13 = Interlaced from bottom
14 = Push from left
15 = Push from right
16 = Push from top
17 = Push from bottom
18 = Rotate to the left
19 = Rotate to the right
20 = Blend the rooms
21 = Fade out and in

transition_steps Indicates the number of steps in the transition. The more steps, the longer the transition takes. Default is 80.
transition_define(kind,name) You can actually create your own transitions. To this end you must define a script (possibly in an extension package) to do the transition. With this function you can then add the transition to the system. kind is the index of the transition (either a new one or an existing transitions). name is the name of the script. Note that the name of the script is a string! So there must be quotes around it. Note that this is really advanced stuff. The script must take five arguments: a surface with the image of the previous room, a surface with the image of the next room, the width of the surfaces, the height of the surfaces, and the fraction of the transition (between 0 and 1). It must then draw the image using the two surfaces.
transition_exists(kind) This function returns whether a transition of the indicated kind exists.