Edit expression guide

I'm going through all the guides again and improving their logical layout, grammar, spelling, etc ...
Still a work in progress, so don't merge just yet.

For the expression guide,

I'm confused on how the buffer works on one of the example expressions:

```html
<div data-list="user in users [buffer: 2, max: 10]"></div>
```

What would be an example of the outputted HTML?