How does the Username Regular Expression work?
 

I've been trying to understand how this feature works: vBulletin Options > User Registration Options > Username Regular Expression:

If I place a valid code inside the input field of Username Regular Expression, will registration be denied for anyone not following the requirements of the code?

Specifically I'm looking to require a first and last name upon registration and was wondering if this code will do the trick?

Code:
^[a-zA-Z'-]+\s+([a-zA-Z'-]+\s*)+
If not, does anyone know how to properly code the Username Regular Expression to achieve this?

TIA