string.format

[ARYDER]

Hi! So, I'm working on a license plate system. 
For me, this is a completely new kind of "coding" and, in general, I already know a lot and can do a lot. But I'm still struggling with some of the formatting stuff. 

For example, let's take the format of German license plates:

One/two/three letters in front of the stickers
One/two letters after the stickers
One to four digits after all letters, but the total number of license plate characters does not exceed 8

is it possible to fit the formatting of such a string into a single string.format formula without using if/then

 

I am currently using several formats for string with one/two/three letters at the beginning and, of course, I limit the maximum number of characters entered. Smth like this:

^(%a)(%a+)%d+$
^(%a%a)(%a+)%d+$
^(%a%a%a)(%a+)%d+$


Is there anything else I don't know?

Edited June 29 by sadvely