I am on the fence about this, but worth mentioning. I would probably lean towards introducing a variable or constant to represent the regex, a flavour of an [explaining variable](http://sourcemaking.com/refactoring/introduce-explaining-variable) (or const)

I am only on the fence here because the regex is quite simple. Though explaining exactly what the regex is doing isn't bad.

```ruby
WHITESPACES = /\A\s*\z/

token_output =~ WHITESPACES
```