General - See below for mesh details. The names a.drainX and a.outsideviewX, where X is a number, are 'MAGIC' names that mean something to the Trainz game engine. The other names here are arbitrary and do nothing special beyond being attachment points.
Draincocks
Contained herein are 2 meshes - drain1.im and drain2.im Each has 1 attachement point a.drain1 (drain1.im) and a.drain2 (drain2.im) These meshes can be attached to a steam locomotive to allow the use of ALT D (open/close draincocks). Note that the locomotive's config file will have to be edited not only to attach them meshes, but also to have additional 'smokeX' containers assigned to a.drain1 and a.drain2 to produce the visible effect of the steam.
Outside Views
There are 3 outside view meshs, outsideview0.im has a.outsideview0 - outsideview1.im has a.outsideview1 - outsideview2.im has a.outsideview2 place as attachments to any available attachment point on the main body, and use 'position' and 'orientation' tags to move it to the desired location. Cycling thru the cabview cameras will automatically include these locations in order. I typically place them as 0=Engineer headout 1=Front Coupler view 2=Fireman headout.
Leaky Cylinders
leak0.im (a.leak0) and leak1.im (a.leak1) are for adding points for leaking steam from the cylinders. Again, connect to an attachment point on the body, and use 'position' and 'orientation' to move them where desired
Safety Valve
safetyvalve.im (a.safety) is for safety valve effects. Again, connect to an attachment point on the body, and use 'position' and 'orientation' to move them where desired
Driver Meshes
driver0.im (a.driver0) and driver1.im (a.driver1) are supplied for adding the attachment point(s) needed for a driver character to appear in the cab. Use 'position' and 'orientation' to move them where desired