Limitations on - and + operators

From Sal Palacios (via email):

Im noticing it throws errors for syntax that seems to be legit .. For example it give error on the following syntax which should be ok:

```
title:foo -title:bar
```

Or any kind of grouping with a `+` or `–` in front of it like such

```
-(foo bar)
```

```
+(foo bar)
```
