I've wanted to use Emacs to edit relations for a while. I could then make a "mode" that formats relations so things are easy to see, do automatic indentation, etc. Unfortunately, I could never figure out how to get the relations data into Emacs from within Creo. There's no "file" to pass to it for editing, at least nothing that I could find. I gave up on this dream years ago and it still annoys me, especially since I've been doing a huge amount of relations editing in the last couple of years.
Try using notepad++ from https://notepad-plus-plus.org/
You can create your own "language" for the Relations and Pro/Program tools.
If you search these community pages, you may find some languages already defined.
I've been asking about using Emacs for relations editing for a long time. I have never been able to get it to work. The problem seems to be getting the program to start up and be "fed" the file that is being edited. If I could figure out how to bring up Emacs with the relations, I could easily put together a mode file that would do syntax highlighting (colors for functions, key words, comments, etc.) It would be very nice, because then you would also have all of the wonderful editing functions that Emacs provides.
Other than that, I've also seen a lot of discussion of using Notepad+ to edit, with syntax highlighting possible.
As for Linux, unfortunately Creo long ago abandoned support for Unix-based operating systems, due to the fact that it's a tiny portion of the market and Windows is so dominant.
You could try TextPad (Helios Software Solutions). It's my favourite tool for java programming, with excellent syntax highlighting features. You can use your own customised syntax definition file.
Here is the result of a quick experiment I tried after reading your post ...
I only tried this quickly for an *.als file.
I think I'll look in to this further for my own benefit.
Thanks for posting.