Return Solution Version in an Expression Box
Don't claim to understand this 100%, but I do know it works. Put this formula inside a formula dialog box for an expression box on your form, and when you invoke it it'll show you the current solution version - without having to write code!
substring-before(substring-after(/processing-instruction(), 'solutionVersion="'), '"')
Edited on 10/7 per input from Karsten, thanks!