Ridders, I discovered an easier way to do that, and your String function is part of it.
1. Build a constant length string of dots
Dots = STRING(desired-length, ".")
2. Insert first part
Mid(dots, 1, Len(PFX) ) = Pfx
3. Insert second part.
Mid(dots, Len(Dots) - Len(Sfx), Len(Sfx) ) = Sfx
I've used this approach many times. For those not familiar with the STRING function, here is a reference.
https://support.office.com/en-us/article/string-function-4808c43b-7640-4334-87fc-457499c185b1
A further comment is in order: You must be careful when using the tab character. You see, it is a holdover from the days of ASCII Teletypes. (Trust me, as a Navy contractor and as a 50-year programmer, I've seen Teletypes.) The TAB, being a carriage control character, relies on TAB STOPS, which originally were mechanical things that were, by tradition set every 8 columns. But if you had special forms loaded to your printing device, the tab stops would be set to the starting edge of each field on your special forms. Ah, for the days of fan-folded special card-stock printers... but I'm getting a bit nostalgic here.
Anyway, for a display device, a TAB means exactly what the designer of the FONT wanted it to mean, and sometimes that is NOTHING. So when you put a TAB character in a string and display it, you are at the mercy of the font, and as is well known, computers have no mercy.
That might not be the case when you actually PRINT something that contains a TAB because the printing device's driver might implement that TAB in software. Therefore, when using a TAB for something, consider WHERE you will use it. It won't always work because on a display device are there no tabs that you didn't set yourself.
In fact, consider MS WORD. You can set TAB stops there because WORD is SIMULATING a physical printer to give you WYSIWYG displays. There, TAB means something but only because it is TRYING to look like a printer's output.
If you create a text file using OPEN file FOR OUTPUT as #1 (or something similar) and use a PRINT #1 to write text to the file, then the TAB character acts as though you have software tab stops. But again, it is EMULATING printer behavior.
Moral of the story? If you aren't going to output to a real printer with real carriage control, use some other method to align your text output.