Hi all, hoping I'm in the right forum for this. One of my roles within my organisation is leading some of the solution architecture for our MS Cloud for Healthcare dynamics solution. But it is a generalised Dynamics question. 
 
I'm trying to work out the code for how to validate a number (its actually Medicare number, 10 digits with some other rules that we can ignore for the time being). There is the standard OOTB number length limiter, but no minimum length etc. I was hoping a simple expression typed into the formula bar for the MaxLength property would work (see below). Otherwise I'd just place an icon so that a tick appears next to Medicare Number if it is not less than and not greater than 10 digits. 
 
The trouble is, I can't seem to find what I need online in forums etc. that allows me to enter an expression that actually doesn't error.
 
Can anyone advise an easy code script for this?