How to achieve an Autocomplete Field Validation rule in VBS

Summary:

Field Validation AC rule needs rebuilding in VBS - need some guidance on this as suspect it needs Advanced Expression

Content (please ensure you mask any confidential information):

We have an AC Field Validation rule on the Worker Assignment object to validate the format of some Assignment DFF's.

I need to replicate in VBS and have had a go but I think I need to do an Advanced Expression on my Validation rule to check the format of the data and I do not know how to do this (we have not used advanced expressions before and we can not find much information on how to do them).