Jan Rif.?
Into 5 files? Select one by one? In your output program, that is?
Since, I want to make this clear, my proning here in this forum to break up your things into a rather big numer of MI files / topics is NOT born out of an incapacity of MI to handle big files, but only out of my experience of "natural hoisting" if I may say so, MI's search feature allowing for this splitting up.
But my experience with some big MI files is very good, here in MI splitting up UNIFORM stuff into several should thus NOT be necessary (I hope).
If you must select 5.000 items in your output program in order to split your file, though, apply a macro program for doing so. There are some macro programs that allow for some trial period.
I use Hot Keyboard but beware first encounter with this program is awkward; I use it altogether since HK is able to do key combinations like Alt-Tab for example which very few competitors are able of.
But you could tell what's your output program is, and give all the necessary steps, and I'd give you the HK commands in order to realize that little program, so you wouldn't have to learn some macro program just in order to do this export job.
HK is from Russia and a very serious macro program I've been using for some years now. There are some other macro programs that have much more accessability (i.e. are much easier to have something run within a short time) but soon show limitations that cannot be overcome. (And some macro programs are not stable, not reliable.)
(But HK has some faults also, and the programmer KNOWS them - you bet I made a list of them for him

- so perhaps before buying, wait for the next update, the last one being some years old.)
And since we are at it, another hint for everyone: If your macro program is not reliable, insert short delays depending on your comp, let's say 100 msec here, 300 msec there, but after EVERY command in the macro, and depending on what that command is asked to do; many macro programs will gain a totally new reliability by this.
Have a look at Perfect Keyboard, it's from Czechia. I tried it some years ago, it wasn't stable, and in their forum, there are people complaining about some stability issues, but its programmability is far ahead HK (in its current state). There is one really tremendous macro program, that's WinTask - I've never seen anything this good, including a 1,000 dollar program from the U.S. - but then, WT is 249 euro, more than 300 dollars - but WT is worth it when you need automation regularly...
Tell the steps in the output program, and I'll see if a little HK program can do it (I do not remember the - SEVERE???- limitations of the HK trial version)...
but it would be really a pity if you couldn't do your things in MY because you could not enter your stuff into it, so that needs help!
But then, what is the program you wanne leave?
It's a little world, our outliner community...

How the h*** are doing people without any outliner?! Poor them!
