I'm sorry if this isn't a 100% entlib question but I'm having problems creating a regexp for my regex validator.
My buisnessobject has a string property that either is null, or it has some contents that only can contain certain characters.
I've tried with: ^$|^[\w\s\.\-,':]*$
I've bolded the pipe-character to show that it's two different valid sets.
I can do it with a Or Composite Validator where I have a negated Not Null Validator and a Regex Validator, but I would like to only have to one validator so I can keep the number of validators down a little.