[Scala] Various stateful bailout bugs

[djspiewak]

Random best practice that's worth documenting somewhere…  When you have any sort of stateful context chain, make sure each link in the chain ends with the following:

- match: (?=\S)
  pop: true

Anything you don't recognize, you should just bail on.

Another best practice: don't accidentally match on double word boundary by having a trailing pipe character.

[FichteFoll]

Another best practice: don't accidentally match on double word boundary by having a trailing pipe character.

I, too, have been guilty of this.

[wbond]

I agree that some best practices would be good to add. I've opened #757 where you can write things down. I'll write them up and add to the docs at some point.