Add a NotANumber function

Because CRM does not provide a way to format numbers. we sometimes have to display them in a character entity. For example, if you want to store a year value, in a numeric field it will be displayed like this: 2,013 So we have to store it in a character field instead and add some validation. A simple NotANumber function would be a very useful way to validate these fields. I may have missed the ability to do this - the conversion functions don't seem to help - maybe it could be done with regex, but I can't work out how.