Dimension reference pattern not explained in wiki or forum answers

I have read every word of the wiki topics on dimensions, and many relevant forum posts. If I missed the answer to the question below, pls refer me.  I understand why dimensions exist and I need at least one. I have used dimension-like features in other accounting systems.

For the company, I am able to create dimensions. When creating a dimension, it asks for the dimension reference number. As I experiment, it seems to want the following pattern (like the default number it inserts):
number followed by a slash / followed by a number (for example:  301/2019).
The second number is not a date since it will accept for example: 4023
I prefer not to have the slash and second number. 

The first number cannot begin with a letter, and seemingly must be followed by the slash.

I don't need letters but am just trying to understand the reference pattern. So I don't understand how this forum post (https://frontaccounting.com/punbb/viewtopic.php?pid=4753#p4753) can say, "So when you created the dimension, you could have put MJ125 in the first reference field." 

I don't see anywhere to edit/set the PATTERN of the dimension reference, nor any definition of acceptable dimension reference patterns in the wiki. 

A couple of the forum answers tell people to read the wiki on dimensions, which I did. But I don't see anything relevant there. Again, if I'm missing something, please refer me.

I understand that dimension references apparently can be edited with phpmyadmin or similar tool, but am trying to avoid that and work from the GUI and consistently with how FA works natively.

Thank you.