A quick search in the .exe determined the following tags exist:
COMMENT
DISPLAYTIME
FADESPEED
FONTCOLOR
BACKGROUND
PAGE
SCREENLOWERLEFT
SCREENCENTER
SCREENBOTTOM
SCREENTOP
SCREENRIGHT
SCREENLEFT
Separated into two groups the first group can be set in each </PAGE>. You can have multiple pages (or "screens") per .txt file.
The second group positions the text in the screen. You cannot use more than one of these between pages and they affect the text after the tag.
Example:
Code
</COMMENT LOL RANDOM TEXT>
</FADESPEED 1000>
</DISPLAYTIME 8000>
</BACKGROUND glue\palpa\ProtossA.pcx>
</FONTCOLOR glue\palpa\tfont.pcx>
</SCREENRIGHT>
"ESCAPE FROM AIUR"
Isolated Protoss base on the planet Aiur
</PAGE>
</FADESPEED 1000>
</DISPLAYTIME 8000>
</BACKGROUND glue\palpa\ProtossA.pcx>
</FONTCOLOR glue\palpa\tfont.pcx>
</SCREENRIGHT>
"ESCAPE FROM AIUR"
Isolated Protoss base on the planet Aiur
</PAGE>
That file is a single page, it will show the text after SCREENRIGHT right-aligned and for a duration of 8 seconds. Then it will fade to black and show blackness for 1 second before sending you to mission briefing. It will also use the specified background and the respective tfont.pcx to color the text. Using a non corresponding background and/or font file will, of course, result in weird colored text. (mispalleted)
You can also use multiple pages and vary the formatting and background/between them like this:
Code
</COMMENT LOL RANDOM TEXT>
</FADESPEED 1000>
</DISPLAYTIME 8000>
</BACKGROUND glue\palpa\ProtossA.pcx>
</FONTCOLOR glue\palpa\tfont.pcx>
</SCREENRIGHT>
LOL FIRST PAGE
</PAGE>
</COMMENT LOL RANDOM TEXT AGAIN>
</FADESPEED 5000>
</DISPLAYTIME 25000>
</BACKGROUND glue\palpb\ProtossB.pcx>
</FONTCOLOR glue\palpb\tfont.pcx>
</SCREENCENTER>
LOL SECOND PAGE
</PAGE>
</FADESPEED 1000>
</DISPLAYTIME 8000>
</BACKGROUND glue\palpa\ProtossA.pcx>
</FONTCOLOR glue\palpa\tfont.pcx>
</SCREENRIGHT>
LOL FIRST PAGE
</PAGE>
</COMMENT LOL RANDOM TEXT AGAIN>
</FADESPEED 5000>
</DISPLAYTIME 25000>
</BACKGROUND glue\palpb\ProtossB.pcx>
</FONTCOLOR glue\palpb\tfont.pcx>
</SCREENCENTER>
LOL SECOND PAGE
</PAGE>
That will show you the text LOL FIRST PAGE with the same duration, alignment and background of the last time AND after the fade transition it will show you the text LOL SECOND PAGE for 25 seconds at the very center of the screen, with a different background then it will fade to black and show you blackness for 5 seconds.
That's all the tags I could find (I got creative and tried some others but I got nowhere) You cannot use two formatting tags, it will just show you the first one and ignore all others.
In addition to that you can use text colors inside of this. Since they're just .txt files doing it the "proper" way won't work. With tags like <01> <04> etc... They WILL work if you use a single character code, just like the old ones we used to use that just looked like squares. You can either get them from SCMDraft or Starforge LMAO (Sorry, Clork_

I have no time to make said list atm. I will in the future, but if anyone wants to post one or knows where to find it that'd be a nice complement to this topic.
These are all my findings on .txt files that I forgot to post like a week ago. I'll also be updating the wiki soon (tm). Cheers.
fuck you all