Let's give lookaheads a shot.

```javascript
> 'hello mel'.match(/e(?=ll)/)
[ 'e',
  index: 1,
  input: 'hello mel' ]
```

You'll see it only matches e's that are followed by two l's, but those l's are not included in the match.


```javascript
> slides = '# first\n\n--\n\n# second\n\n-- dog\n\nhello, world'
'# first\n\n--\n\n# second\n\n-- dog\n\nhello, world'
> console.log(slides)
# first

--

# second

-- dog

hello, world

> slides.split(/\n(?=\-\-)/)
[ '# first\n',
  '--\n\n# second\n',
  '-- dog\n\nhello, world' ]
```