[Flow] How To use RegularExpressionValidator?

[Christian Loock]

Hi,

I am trying to add a regular expression validator to one of my models 
properties:

@Flow\Validate(type="RegularExpression", regularExpression="/^[^_]*_[^_]*_[^_]*$/")


This throws the following error:


    #1339163902: Required validation option not set: regularExpression


How do I pass arguments to a validator to make it work?